I note it says in the wiki that: "I need a new one, what should I get!" comes
up in some form almost every day on uk.d-i-y, but couldn't find enough
information to clench the deal, one way or the other.

My wife and I are living in a two bedroomed bungalow - there's nobody else
living there except the cat! The central heating is old - if the pencilled
date on the back of the controller I replaced recently is anything to go by
it dates from 1996.

We had a quote recently from a local plumber who advocated a combi - which
I've always been convinced from various things I've read (probably here) that
they can be problematic - but he said that modern combis are much better than
their predecessors and would be highly suited to our needs. He also pointed
out that he has a combi in his 4 bedroom property and has no problems with
it.

We then got another quote from someone who is clearly prejudiced against
combis! Apart from additional strain on the old pipework - which we are well
aware of - he said that the increased pressure can damage the non-return
valve in dual fill washing machines (ours is currently a dual-fill Hotpoint)
but that we wouldn't be able to run hot water from two taps at the same time!

This could be a worry if we couldn't wash our hands (or whatever) every time
the washing machine was filling or the other is running a bath. Can this
really be true?

Quote No. 1 includes an Ideal Logic+ 30kW boiler whilst No. 2 is for a
Worcester Bosch 15ri boiler. No. 1 includes quotes for both combi and non
combi options (but does give any indication of which non-combi boiler would
be fitted) and No. 2, as might be expected, doesn't have a second option!

How do these boilers compare - assume No. 1 would use a non-combi version of
the same boiler?

All comments gratefully received!

Terry
--

Terry

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On 20/05/17 13:35, Terry Casey wrote:
I note it says in the wiki that: "I need a new one, what should I get!" comes
up in some form almost every day on uk.d-i-y, but couldn't find enough
information to clench the deal, one way or the other.

My wife and I are living in a two bedroomed bungalow - there's nobody else
living there except the cat! The central heating is old - if the pencilled
date on the back of the controller I replaced recently is anything to go by
it dates from 1996.


Does it work though?


We had a quote recently from a local plumber who advocated a combi - which
I've always been convinced from various things I've read (probably here) that
they can be problematic - but he said that modern combis are much better than
their predecessors and would be highly suited to our needs. He also pointed
out that he has a combi in his 4 bedroom property and has no problems with
it.


He has a deal with comnbi supplires.

We then got another quote from someone who is clearly prejudiced against
combis! Apart from additional strain on the old pipework - which we are well
aware of - he said that the increased pressure can damage the non-return
valve in dual fill washing machines (ours is currently a dual-fill Hotpoint)
but that we wouldn't be able to run hot water from two taps at the same time!


Well thats ******** too.

This could be a worry if we couldn't wash our hands (or whatever) every time
the washing machine was filling or the other is running a bath. Can this
really be true?

Mate, the combi I have here currently wont even supply enough hot water
to drive ONE hot tap, bath or shower.,

Quote No. 1 includes an Ideal Logic+ 30kW boiler whilst No. 2 is for a
Worcester Bosch 15ri boiler. No. 1 includes quotes for both combi and non
combi options (but does give any indication of which non-combi boiler would
be fitted) and No. 2, as might be expected, doesn't have a second option!

How do these boilers compare - assume No. 1 would use a non-combi version of
the same boiler?

All comments gratefully received!

Terry


Bite the bullet and do the proper job, Mains pressure hot water tank fed
from whatever boiler you have and if in a hard water area all fed via a
pukka ion exchange softener.

Then never have a hot water shortage ever again



--
€œIt is hard to imagine a more stupid decision or more dangerous way of
making decisions than by putting those decisions in the hands of people
who pay no price for being wrong.€�

Thomas Sowell

The Natural Philosopher wrote:
On 20/05/17 13:35, Terry Casey wrote:
I note it says in the wiki that: "I need a new one, what should I
get!" comes up in some form almost every day on uk.d-i-y, but
couldn't find enough information to clench the deal, one way or the
other. My wife and I are living in a two bedroomed bungalow - there's
nobody else living there except the cat! The central heating is old
- if the pencilled date on the back of the controller I replaced
recently is anything to go by it dates from 1996.


Does it work though?


We had a quote recently from a local plumber who advocated a combi -
which I've always been convinced from various things I've read
(probably here) that they can be problematic - but he said that
modern combis are much better than their predecessors and would be
highly suited to our needs. He also pointed out that he has a combi
in his 4 bedroom property and has no problems with it.


He has a deal with comnbi supplires.

We then got another quote from someone who is clearly prejudiced
against combis! Apart from additional strain on the old pipework -
which we are well aware of - he said that the increased pressure can
damage the non-return valve in dual fill washing machines (ours is
currently a dual-fill Hotpoint) but that we wouldn't be able to run
hot water from two taps at the same time!

Well thats ******** too.

This could be a worry if we couldn't wash our hands (or whatever)
every time the washing machine was filling or the other is running a
bath. Can this really be true?

Mate, the combi I have here currently wont even supply enough hot
water to drive ONE hot tap, bath or shower.,

All this proves is that you have low mains pressure


Quote No. 1 includes an Ideal Logic+ 30kW boiler whilst No. 2 is for
a Worcester Bosch 15ri boiler. No. 1 includes quotes for both combi
and non combi options (but does give any indication of which
non-combi boiler would be fitted) and No. 2, as might be expected,
doesn't have a second option! How do these boilers compare - assume No. 1
would use a non-combi
version of the same boiler?

All comments gratefully received!

Terry


Bite the bullet and do the proper job, Mains pressure hot water tank
fed from whatever boiler you have and if in a hard water area all fed
via a pukka ion exchange softener.

Then never have a hot water shortage ever again

Yes, cos storing hot water in a tank until you use it is better than having
it on demand.
My combi is ten years old, never been serviced and supplies continuous hot
(hard) water every time the tap is turned on, likewise the mixer shower,
which is powerful enough to actually hurt if it's on full.
No water softener ever been in this house
To the OP, get a combi if you have reasonable mains pressure, if it comes
out of the tap like someone having a ****, go the other option

On Sat, 20 May 2017 13:56:06 +0100
"Phil L" wrote:

No water softener ever been in this house

In East Anglia, it is stupid to not have a water softener.
Other parts of the country can do perfectly well without them.

--
Davey.

In article ,
Terry Casey wrote:
All comments gratefully received!

If you already have a storage system which you're happy with, fitting a
replacement boiler for that is not only going to save money, but be easier
than changing to a combi.

The problem may be finding an installer who does think of your needs and
likes, than just his own profit.

--
*If PROGRESS is for advancement, what does that make CONGRESS mean?

Dave Plowman London SW
To e-mail, change noise into sound.

In article , says...

If you already have a storage system which you're happy with, fitting a
replacement boiler for that is not only going to save money, but be easier
than changing to a combi.

The problem may be finding an installer who does think of your needs and
likes, than just his own profit.

In fairness, the first one has also included a quote for a like-for-like (but
condensing) replacement which is £350 less than the combi approach.

--

Terry

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On 5/20/2017 1:35 PM, Terry Casey wrote:
I note it says in the wiki that: "I need a new one, what should I get!" comes
up in some form almost every day on uk.d-i-y, but couldn't find enough
information to clench the deal, one way or the other.

My wife and I are living in a two bedroomed bungalow - there's nobody else
living there except the cat! The central heating is old - if the pencilled
date on the back of the controller I replaced recently is anything to go by
it dates from 1996.

We had a quote recently from a local plumber who advocated a combi - which
I've always been convinced from various things I've read (probably here) that
they can be problematic - but he said that modern combis are much better than
their predecessors and would be highly suited to our needs. He also pointed
out that he has a combi in his 4 bedroom property and has no problems with
it.

We then got another quote from someone who is clearly prejudiced against
combis! Apart from additional strain on the old pipework - which we are well
aware of - he said that the increased pressure can damage the non-return
valve in dual fill washing machines (ours is currently a dual-fill Hotpoint)
but that we wouldn't be able to run hot water from two taps at the same time!

This could be a worry if we couldn't wash our hands (or whatever) every time
the washing machine was filling or the other is running a bath. Can this
really be true?

Quote No. 1 includes an Ideal Logic+ 30kW boiler whilst No. 2 is for a
Worcester Bosch 15ri boiler. No. 1 includes quotes for both combi and non
combi options (but does give any indication of which non-combi boiler would
be fitted) and No. 2, as might be expected, doesn't have a second option!

How do these boilers compare - assume No. 1 would use a non-combi version of
the same boiler?

All comments gratefully received!

Terry


I sometimes use a small holiday cottage on the Isle of Wight which has a
combi that seems to do the job: enough hot water for a shower, sink
water hot enough for washing up properly, and the CH is OK too.

HOWEVER, I've had two combis in my admittedly larger and sprawling 18th
Century cottage and they were both hopeless. Apart from generally
inadequate hot water not particularly good heating, they were not reliable.

I ended up putting a separate electrically heated cylinder for DHW.

More recently I replaced the lot with a traditional "system" boiler
(Vaillant) and a new unpressurised hot water cylinder but the same
radiators. Finally I have enough heat and water from gas. I do have a
Stuart Turner double pump for the shower, and a second Stuart Turner
"single" for the DHW, which gives me a decent flow rate particularly for
the bath. A shower pump is certainly not a bad idea if you don't have
much head.

I know TNP has good arguments for pressurised hot water, and if I was
starting from scratch with an unlimited budget this is probably what I
would do. But it comes at a price, and may need more servicing.

I would personally only consider Vaillant and Worcester Bosch, on the
basis of advice both here and in Which?

As you have probably surmised, the anti-combi guy is probably a bit of a
bull****ter, but what he says about hot water flow rates is reasonable.

I guess a "system" installation with a separate hot cylinder is going to
be a bit more expensive.

How old is the bungalow, and what's the insulation and draft-proofing
like? Semi or detached? There are calculators on-line to help estimate
your heating requirements which could vary by a factor of 2. Or if you
are on an estate, ask your neighbours what boilers they have, and
whether they are adequate.

In article ,
newshound wrote:
As you have probably surmised, the anti-combi guy is probably a bit of a
bull****ter, but what he says about hot water flow rates is reasonable.

I guess a "system" installation with a separate hot cylinder is going to
be a bit more expensive.

I was assuming that already exists.

If doing a blank canvass install, a combi may well be the most economical
option. But where a storage system already exists and is OK a system
boiler should be cheaper and a lot less work.

--
*Despite the cost of living, have you noticed how it remains so popular?*

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
says...

As you have probably surmised, the anti-combi guy is probably a bit of a
bull****ter, but what he says about hot water flow rates is reasonable.


As far as cold water pressure goes, there is good pressure from the kitchen
cold tap and we also have an instant electric water heater for the shower.

I have noticed that if the washing machine or dishwasher is running while I'm
having a shower with the hot water temperature nice and high, as the demand
from the kitchen appliance turns on, although I'm not aware of a pressure
drop, the temperature can suddenly nudge up from comfortably hot to
uncomfortably hot.

However, the anti-combi guy seemed to be implying that the hot water flow
from the combi would be restricted to maintain the temperature if demand
increased but I find that a bit difficult to swallow. In any case, his quote
was considerably higher than the first one, higher even than the combi quote,
so we definitely wouldn't be using him, whatever we decide. He did, however,
sow sufficient seeds of doubt to get us querying the whole combi set-up ...

I guess a "system" installation with a separate hot cylinder is going to
be a bit more expensive.


We already have a cylinder which is heated by the boiler or an immersion
heater if the CH is turned off.

How old is the bungalow, and what's the insulation and draft-proofing
like? Semi or detached? There are calculators on-line to help estimate
your heating requirements which could vary by a factor of 2. Or if you
are on an estate, ask your neighbours what boilers they have, and
whether they are adequate.

Detached, although the gap between the side wall and an adjacent garage has
been roofed over and turned into two narrow storage areas, one with access
from the front and one from the back. 1961. There is 6" of insulation in the
loft or possibly 8". Adam will know because he fills the bath with the stuff
every time he goes up there!

Draft proofing is good although the aluminium framed double glazing leaves a
lot to be desired as there is obviously no thermal barrier between inside and
out. That is next on the agenda for replacement.

Whether there is any cavity wall insulation, we don't know. There are no
obvious signs of anything being done

--

Terry

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Dave Plowman (News) wrote:
In article ,
Terry Casey wrote:
All comments gratefully received!

If you already have a storage system which you're happy with, fitting a
replacement boiler for that is not only going to save money, but be easier
than changing to a combi.

The problem may be finding an installer who does think of your needs and
likes, than just his own profit.


A personal observation going from a 1987 installed conventional system
in a (then) new 4 bed detached.

A WB 34KW Greenstar boiler is more than adequate and shows no sign of
struggling to meet the thermal demand for HW with multiple showers
operating.

A lot of pipework & HW cylinder was removed and the airing cupboard
recovered in full as storage. Roof insulation could now be improved as
no need to worry about the cisterns freezing.

No issues with leakage from (now) pressurised 30 year old HW/CH system
(8mm microbore). This was my biggest worry as the water pressure round
here is highish (3 bar).

The thermostatic shower valves and newer taps now operate correctly with
the higher pressure. It was a bit hit and miss before getting them
started enough to kick in the shower pump.

There is a noticable issue with HW water flow rate upstairs &
interaction between showers & filling the bath is a bit slow. This is
probably down to re-using the original 15mm pipe work. It would have
been better to have replaced this with 22mm.

Reliability OK so far 2 years in but needs paid annual inspection to
maintain the 7 year guarantee - the old Potterton Netaheat boiler needed
about £200 in DIY repair over 25 years (2 replacement fans), doesn't
look possible with this one.

Been a noticable drop in gas consumption but not huge as the property is
well insulated and the old boiler was not that bad (rated 69%).

HTH

Chris K

On 20/05/2017 13:35, Terry Casey wrote:
I note it says in the wiki that: "I need a new one, what should I get!" comes
up in some form almost every day on uk.d-i-y, but couldn't find enough
information to clench the deal, one way or the other.

My wife and I are living in a two bedroomed bungalow - there's nobody else
living there except the cat! The central heating is old - if the pencilled
date on the back of the controller I replaced recently is anything to go by
it dates from 1996.

We had a quote recently from a local plumber who advocated a combi - which
I've always been convinced from various things I've read (probably here) that
they can be problematic - but he said that modern combis are much better than
their predecessors and would be highly suited to our needs. He also pointed
out that he has a combi in his 4 bedroom property and has no problems with
it.

We then got another quote from someone who is clearly prejudiced against
combis! Apart from additional strain on the old pipework - which we are well
aware of - he said that the increased pressure can damage the non-return
valve in dual fill washing machines (ours is currently a dual-fill Hotpoint)
but that we wouldn't be able to run hot water from two taps at the same time!

This could be a worry if we couldn't wash our hands (or whatever) every time
the washing machine was filling or the other is running a bath. Can this
really be true?

Should be OK unless you have hand washing OCD. Combis are adequate for
small or medium flats/houses unless you have more than one bathroom.

--
Max Demian

Like you I have always been sceptical about combi boilers but have been pleasantly surprised by the performance of the one we inherited when we moved into our present 2 bedroomed bungalow, which has 200mm loft insulation, cavity wall insulation and we recently upgraded some old UPVC windows and installed a light weight insulated roof on a conservatory which is an extension of the second bedroom. Our boiler is a Worcester Bosch 28i junior and heating wise has coped very well even up here in the Pennines. DHW can be a slight problem, the boiler supplies two basins, kitchen and bathroom and also a bath. Running the two basin taps is fine a momentary drop in temp if one is turned on after another. The only issue is the bath which can take an age requiring careful regulation but then again we only shower. Both our washing machine and dish washer are cold fill only. We are soon going to upgrade the bathroom and will replace the current electric shower with an electronic one which will take it's hot feed from the DHW supply and I am confident it will cope. What I am pleased about is that our heating bills have halved compared to our previous 3 bed semi with a condensing system boiler. Admittedly we have two less rooms to heat and a much smaller corridor and the last house did not have cavity wall insulation, but I feel the a good proportion of the savings is due to the efficiency of the boiler. For the likes of bungalows a combi seems to make sense and if ours packed up tomorrow I would gladly replace it with another. One other benefit is we have gained a useful airing cupboard by not having a cylinder despite having the boiler mounted there.

Richard

On 20/05/2017 16:54, Terry Casey wrote:


Whether there is any cavity wall insulation, we don't know. There are no
obvious signs of anything being done


I seem to remember that you do have cavity wall insulation. Have a look
in the outside electric cabinet and where I ran the meter tails up the
cavity.



--
Adam

Do you have a suitable size gas pipe to the location? I needed to re-pipe
in 22mm with minimal bends. A combi needs a lot of gas and a good flow. My
earlier conventional boiler took less - for longer and 15mm pipe was ok.

On 20/05/17 17:51, Max Demian wrote:
Should be OK unless you have hand washing OCD. Combis are adequate for
small or medium flats/houses unless you have more than one bathroom.


Given you can get combis up to 35-42kW (WB) they should be adequate for
2 bathroom properties. WB even do a floor standing combi with insane DHW
flow.

Some combies also have a small water store that they keep hot that helps
with occassional demand.

"Terry Casey" wrote in message
...
I note it says in the wiki that: "I need a new one, what should I get!"
comes
up in some form almost every day on uk.d-i-y, but couldn't find enough
information to clench the deal, one way or the other.

My wife and I are living in a two bedroomed bungalow - there's nobody else
living there except the cat! The central heating is old - if the pencilled
date on the back of the controller I replaced recently is anything to go
by
it dates from 1996.

We had a quote recently from a local plumber who advocated a combi - which
I've always been convinced from various things I've read (probably here)
that
they can be problematic - but he said that modern combis are much better
than
their predecessors and would be highly suited to our needs. He also
pointed
out that he has a combi in his 4 bedroom property and has no problems with
it.

We then got another quote from someone who is clearly prejudiced against
combis! Apart from additional strain on the old pipework - which we are
well
aware of - he said that the increased pressure can damage the non-return
valve in dual fill washing machines (ours is currently a dual-fill
Hotpoint)
but that we wouldn't be able to run hot water from two taps at the same
time!

This could be a worry if we couldn't wash our hands (or whatever) every
time
the washing machine was filling or the other is running a bath. Can this
really be true?

Quote No. 1 includes an Ideal Logic+ 30kW boiler whilst No. 2 is for a
Worcester Bosch 15ri boiler. No. 1 includes quotes for both combi and non
combi options (but does give any indication of which non-combi boiler
would
be fitted) and No. 2, as might be expected, doesn't have a second option!

How do these boilers compare - assume No. 1 would use a non-combi version
of
the same boiler?

All comments gratefully received!

Terry

I resisted a new combi for years but they are now quite good...you will save
a fortune ....just go for it ....

On Sat, 20 May 2017 13:35:45 +0100, Terry Casey
wrote:

[snip]

I installed a combi boiler (Worcester Bosch) last year and I am a bit
disappointed with it.

The water takes a while to heat up when using Eco mode. I mostly run
without Eco mode (pre-heat is capable of being programmed) so I assume
I am using extra energy to save water.

The bath takes ages to fill. This may however be related to having an
unusual thermostatic mixer tap arrangement that serves the bath and
the shower.

The radiators warm up even when the heating is supposed to be off. I
understand this is because the boiler uses the heating as a heat sink
when it is pre-heating the hot water. Again, I assume this means
wasting energy.

I find the extractor system noisy for a domestic application, but this
may be common to all condensing systems.

The hot water even at its maximum setting is not hot enough. It's
okay for filling sinks and baths in the first place but for a top-up
it is fairly ineffective.

The washing machine is cold fill so this is not an issue. I think
nearly all washing machines are cold fill, so probably your next one
will be. Could you not disable hot fill if this would help?

On 20/05/2017 16:54, Terry Casey wrote:
In article ,
says...

As you have probably surmised, the anti-combi guy is probably a bit of a
bull****ter, but what he says about hot water flow rates is reasonable.


As far as cold water pressure goes, there is good pressure from the kitchen
cold tap and we also have an instant electric water heater for the shower.

I have noticed that if the washing machine or dishwasher is running while I'm
having a shower with the hot water temperature nice and high, as the demand
from the kitchen appliance turns on, although I'm not aware of a pressure
drop, the temperature can suddenly nudge up from comfortably hot to
uncomfortably hot.

However, the anti-combi guy seemed to be implying that the hot water flow
from the combi would be restricted to maintain the temperature if demand
increased but I find that a bit difficult to swallow. In any case, his quote
was considerably higher than the first one, higher even than the combi quote,
so we definitely wouldn't be using him, whatever we decide. He did, however,
sow sufficient seeds of doubt to get us querying the whole combi set-up ...

I guess a "system" installation with a separate hot cylinder is going to
be a bit more expensive.


We already have a cylinder which is heated by the boiler or an immersion
heater if the CH is turned off.

How old is the bungalow, and what's the insulation and draft-proofing
like? Semi or detached? There are calculators on-line to help estimate
your heating requirements which could vary by a factor of 2. Or if you
are on an estate, ask your neighbours what boilers they have, and
whether they are adequate.

Detached, although the gap between the side wall and an adjacent garage has
been roofed over and turned into two narrow storage areas, one with access
from the front and one from the back. 1961. There is 6" of insulation in the
loft or possibly 8". Adam will know because he fills the bath with the stuff
every time he goes up there!


Your loft insulation is pretty good. I think there is a note in the loft
stapled to a roof truss telling you when the second lot of insulation
was fitted.

Loft insulation in the bath is my calling card:-)


--
Adam

On 20/05/17 13:56, Phil L wrote:
The Natural Philosopher wrote:


Mate, the combi I have here currently wont even supply enough hot
water to drive ONE hot tap, bath or shower.,

All this proves is that you have low mains pressure

Compltely and utterly wrong

main pressure is about 8 bar

what i have is a combi that cant heat water fast enough and has
minuscule hott water store


Bite the bullet and do the proper job, Mains pressure hot water tank
fed from whatever boiler you have and if in a hard water area all fed
via a pukka ion exchange softener.

Then never have a hot water shortage ever again

Yes, cos storing hot water in a tank until you use it is better than having
it on demand.

Correct.

My combi is ten years old, never been serviced and supplies continuous hot
(hard) water every time the tap is turned on, likewise the mixer shower,
which is powerful enough to actually hurt if it's on full.

no, it doesn't unless yu have around 50Kw rating


No water softener ever been in this house
To the OP, get a combi if you have reasonable mains pressure, if it comes
out of the tap like someone having a ****, go the other option


oh the water comes out aright. Cold

work out how big a combi needs to be to say dump 400 litres a minute of
water at 60 degrees

then work out how much more expensive that is than a small boiler with a
mains pressure hot water tank

then do the sensible thng



--
The biggest threat to humanity comes from socialism, which has utterly
diverted our attention away from what really matters to our existential
survival, to indulging in navel gazing and faux moral investigations
into what the world ought to be, whilst we fail utterly to deal with
what it actually is.

On 20/05/17 18:24, DerbyBorn wrote:
Do you have a suitable size gas pipe to the location? I needed to re-pipe
in 22mm with minimal bends. A combi needs a lot of gas and a good flow. My
earlier conventional boiler took less - for longer and 15mm pipe was ok.

no gas at all here


--
To ban Christmas, simply give turkeys the vote.

On 20/05/17 18:29, Tim Watts wrote:
On 20/05/17 17:51, Max Demian wrote:
Should be OK unless you have hand washing OCD. Combis are adequate for
small or medium flats/houses unless you have more than one bathroom.


Given you can get combis up to 35-42kW (WB) they should be adequate for
2 bathroom properties. WB even do a floor standing combi with insane DHW
flow.

a 40kw combi costs a lot more than a 10kw system boiler with a mains
pressure tank

Some combies also have a small water store that they keep hot that helps
with occassional demand.



--
To ban Christmas, simply give turkeys the vote.

In article 6,
says...

Do you have a suitable size gas pipe to the location? I needed to re-pipe
in 22mm with minimal bends. A combi needs a lot of gas and a good flow. My
earlier conventional boiler took less - for longer and 15mm pipe was ok.

The gas pipe does indeed need upgrading for a combi and that is included in
the quote we have.

--

Terry

---
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The Natural Philosopher wrote:
On 20/05/17 13:56, Phil L wrote:
The Natural Philosopher wrote:


Mate, the combi I have here currently wont even supply enough hot
water to drive ONE hot tap, bath or shower.,

All this proves is that you have low mains pressure

Compltely and utterly wrong

main pressure is about 8 bar

what i have is a combi that cant heat water fast enough and has
minuscule hott water store


You need a proper combi then, mines a crap make 'Biasi' and you can't hold
your hand under the hot tap when it's on full flow. The boiler is about
25-28kw and the DHW is set to about 60


Bite the bullet and do the proper job, Mains pressure hot water tank
fed from whatever boiler you have and if in a hard water area all
fed via a pukka ion exchange softener.

Then never have a hot water shortage ever again

Yes, cos storing hot water in a tank until you use it is better than
having it on demand.

Correct.

Storing a bathful of hot water in the loft overnight is better than filling
a bath and getting in?


My combi is ten years old, never been serviced and supplies
continuous hot (hard) water every time the tap is turned on,
likewise the mixer shower, which is powerful enough to actually hurt
if it's on full.

no, it doesn't unless yu have around 50Kw rating

26-28 kw and I can half fill the bath if I put the plug in during a shower


No water softener ever been in this house
To the OP, get a combi if you have reasonable mains pressure, if it
comes out of the tap like someone having a ****, go the other option


oh the water comes out aright. Cold

work out how big a combi needs to be to say dump 400 litres a minute
of water at 60 degrees

Why on earth would you need 800 pints of hot water in 60 seconds?

I can fill the bath in about 5 minutes and it's too hot to get in until I've
run the cold into it for a few minutes

then work out how much more expensive that is than a small boiler
with a mains pressure hot water tank

then do the sensible thng

You've obviously had a non functioning combi. I've recently finished work on
four three storey detatched newbuild houses and all of them have a WB 30kw
boiler installed on the middle floor, each one supplies a kitchen, four
showers and four basins and one bath. No problems with any of them

On 20/05/2017 19:44, Phil L wrote:
The Natural Philosopher wrote:
On 20/05/17 13:56, Phil L wrote:
The Natural Philosopher wrote:


Mate, the combi I have here currently wont even supply enough hot
water to drive ONE hot tap, bath or shower.,

All this proves is that you have low mains pressure

Compltely and utterly wrong

main pressure is about 8 bar

what i have is a combi that cant heat water fast enough and has
minuscule hott water store


You need a proper combi then, mines a crap make 'Biasi' and you can't hold
your hand under the hot tap when it's on full flow. The boiler is about
25-28kw and the DHW is set to about 60


Bite the bullet and do the proper job, Mains pressure hot water tank
fed from whatever boiler you have and if in a hard water area all
fed via a pukka ion exchange softener.

Then never have a hot water shortage ever again

Yes, cos storing hot water in a tank until you use it is better than
having it on demand.

Correct.

Storing a bathful of hot water in the loft overnight is better than filling
a bath and getting in?


My combi is ten years old, never been serviced and supplies
continuous hot (hard) water every time the tap is turned on,
likewise the mixer shower, which is powerful enough to actually hurt
if it's on full.

no, it doesn't unless yu have around 50Kw rating

26-28 kw and I can half fill the bath if I put the plug in during a shower


No water softener ever been in this house
To the OP, get a combi if you have reasonable mains pressure, if it
comes out of the tap like someone having a ****, go the other option


oh the water comes out aright. Cold

work out how big a combi needs to be to say dump 400 litres a minute
of water at 60 degrees

Why on earth would you need 800 pints of hot water in 60 seconds?

I can fill the bath in about 5 minutes and it's too hot to get in until I've
run the cold into it for a few minutes

then work out how much more expensive that is than a small boiler
with a mains pressure hot water tank

then do the sensible thng

You've obviously had a non functioning combi. I've recently finished work on
four three storey detatched newbuild houses and all of them have a WB 30kw
boiler installed on the middle floor, each one supplies a kitchen, four
showers and four basins and one bath. No problems with any of them


If all four showers are used concurrently, while someone is also
using hot water in the kitchen then there will be a problem.

It's called the laws of physics. The faster you move cold water
through the combi, the less heat is transferred into it from the
heat exchanger. So choose between showers running like a poor
old sod with a prostate problem or lukewarm water.

And while this is happening all the heating stops.
This can be a problem with an old leaky house.

On 20/05/2017 17:44, ChrisK wrote:
There is a noticable issue with HW water flow rate upstairs &
interaction between showers & filling the bath is a bit slow. This is
probably down to re-using the original 15mm pipe work. It would have
been better to have replaced this with 22mm.

If your mains pressure and flow rate are adequate then 15mm should be
fine. Sounds like you have another problem somewhere.

On 20/05/2017 13:35, Terry Casey wrote:
I note it says in the wiki that: "I need a new one, what should I get!" comes
up in some form almost every day on uk.d-i-y, but couldn't find enough
information to clench the deal, one way or the other.

My wife and I are living in a two bedroomed bungalow - there's nobody else
living there except the cat! The central heating is old - if the pencilled
date on the back of the controller I replaced recently is anything to go by
it dates from 1996.

We had a quote recently from a local plumber who advocated a combi - which
I've always been convinced from various things I've read (probably here) that
they can be problematic - but he said that modern combis are much better than
their predecessors and would be highly suited to our needs. He also pointed
out that he has a combi in his 4 bedroom property and has no problems with
it.

We then got another quote from someone who is clearly prejudiced against
combis! Apart from additional strain on the old pipework - which we are well
aware of - he said that the increased pressure can damage the non-return
valve in dual fill washing machines (ours is currently a dual-fill Hotpoint)
but that we wouldn't be able to run hot water from two taps at the same time!

This could be a worry if we couldn't wash our hands (or whatever) every time
the washing machine was filling or the other is running a bath. Can this
really be true?

Quote No. 1 includes an Ideal Logic+ 30kW boiler whilst No. 2 is for a
Worcester Bosch 15ri boiler. No. 1 includes quotes for both combi and non
combi options (but does give any indication of which non-combi boiler would
be fitted) and No. 2, as might be expected, doesn't have a second option!

How do these boilers compare - assume No. 1 would use a non-combi version of
the same boiler?

All comments gratefully received!

Terry

The first question is do you actually *need* a new boiler? What's wrong
with the existing system? There's no point in replacing it just because
it's "old" if it works ok and if spares are available. [My boiler is far
older than that - and still going strong - although I have updated the
controls.]

A new boiler will almost certainly by be more efficient than an old one
- but the payback time until you have broken even is likely to be quite
a few years, particularly if the new one require more frequent
maintenance. If the controls need updating to make sure that the boiler
doesn't waste energy keeping itself hot when there's no heating or hot
water demand, you can do that for far less than the cost of a new boiler.

If you are convinced that you *do* need a new boiler, the choice between
conventional and combi depends on many factors.

Firstly, do you bath or shower? Even a good combi will take a long time
to fill a bath with hot water compared with a stored hot water system.

Are you desperate to get rid rid of your hot water cylinder in order to
redeploy the space for some other purpose?

Have you got decent pressure and flow from your cold water mains. I
think the figure often quoted is that the mains needs to be able to
deliver at least 14 litres per minute at the point of entry - often the
kitchen tap.

Is your gas pipework up to the job. A combi will consume gas at a very
high rate when heating the hot water (as opposed to the radiators) so
the internal gas pipework may need upgrading.

In my view, there *are* some circumstances in which a combi represents a
good solution - but they're few and far between. I've stayed in one or
two holiday lets in the summer where a combi has been ok, but when I've
stayed with friends and relatives who have a combi in a normal
household, the hot water supply has always been dire!
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

On 20/05/17 20:37, Andrew wrote:
On 20/05/2017 19:44, Phil L wrote:
The Natural Philosopher wrote:
On 20/05/17 13:56, Phil L wrote:
The Natural Philosopher wrote:


Mate, the combi I have here currently wont even supply enough hot
water to drive ONE hot tap, bath or shower.,

All this proves is that you have low mains pressure

Compltely and utterly wrong

main pressure is about 8 bar

what i have is a combi that cant heat water fast enough and has
minuscule hott water store


You need a proper combi then, mines a crap make 'Biasi' and you can't
hold
your hand under the hot tap when it's on full flow. The boiler is about
25-28kw and the DHW is set to about 60


Bite the bullet and do the proper job, Mains pressure hot water tank
fed from whatever boiler you have and if in a hard water area all
fed via a pukka ion exchange softener.

Then never have a hot water shortage ever again

Yes, cos storing hot water in a tank until you use it is better than
having it on demand.

Correct.

Storing a bathful of hot water in the loft overnight is better than
filling
a bath and getting in?


My combi is ten years old, never been serviced and supplies
continuous hot (hard) water every time the tap is turned on,
likewise the mixer shower, which is powerful enough to actually hurt
if it's on full.

no, it doesn't unless yu have around 50Kw rating

26-28 kw and I can half fill the bath if I put the plug in during a
shower


No water softener ever been in this house
To the OP, get a combi if you have reasonable mains pressure, if it
comes out of the tap like someone having a ****, go the other option


oh the water comes out aright. Cold

work out how big a combi needs to be to say dump 400 litres a minute
of water at 60 degrees

Why on earth would you need 800 pints of hot water in 60 seconds?

I can fill the bath in about 5 minutes and it's too hot to get in
until I've
run the cold into it for a few minutes

then work out how much more expensive that is than a small boiler
with a mains pressure hot water tank

then do the sensible thng

You've obviously had a non functioning combi. I've recently finished
work on
four three storey detatched newbuild houses and all of them have a WB
30kw
boiler installed on the middle floor, each one supplies a kitchen, four
showers and four basins and one bath. No problems with any of them


If all four showers are used concurrently, while someone is also
using hot water in the kitchen then there will be a problem.

It's called the laws of physics. The faster you move cold water
through the combi, the less heat is transferred into it from the
heat exchanger. So choose between showers running like a poor
old sod with a prostate problem or lukewarm water.

And while this is happening all the heating stops.
This can be a problem with an old leaky house.



Around 11l/min will supply a shower quite well.

Therefore a combi with 20 odd l/min will serve 2 bathrooms competently.

It's a big combi but it's doable. eg a Worcester Bosch 42CDi Classic
will deliver exactly that (incoming water assumed to be 10C, DHW 40C)

Of course, some people run the DHW hotter - makes no difference here as
it will just be blended with cold at the shower or bath.

On 20/05/2017 13:35, Terry Casey wrote:

I note it says in the wiki that: "I need a new one, what should I get!" comes
up in some form almost every day on uk.d-i-y, but couldn't find enough
information to clench the deal, one way or the other.

Not sure this will help any ;-)

My wife and I are living in a two bedroomed bungalow - there's nobody else
living there except the cat! The central heating is old - if the pencilled
date on the back of the controller I replaced recently is anything to go by
it dates from 1996.

Not *that* old then...

We had a quote recently from a local plumber who advocated a combi - which
I've always been convinced from various things I've read (probably here) that
they can be problematic - but he said that modern combis are much better than
their predecessors and would be highly suited to our needs. He also pointed
out that he has a combi in his 4 bedroom property and has no problems with
it.

Appreciate that some folks are so biased one way or the other, as to be
incapable of being objective!

We then got another quote from someone who is clearly prejudiced against
combis! Apart from additional strain on the old pipework - which we are well
aware of

This is not a combi issue, but a sealed system issue. The vast majority
of new boilers (combi or other type) are designed for sealed system
operation, although there are a few vented options still out there.

IME having converted several systems from vented to sealed, the problems
whilst frequently mentioned are somewhat overstated. Every system I have
encountered has been fine with the raised pressure. The worst case is
that you may need to replace some rad valves. If a rad springs a leak,
then it was near its end of life anyway.

- he said that the increased pressure can damage the non-return
valve in dual fill washing machines (ours is currently a dual-fill Hotpoint)

Not heard that before. Even if true you may have no actual symptom of a
damaged not return valve anyway. If you were really that worried you
could fit a pressure reduction valve prior to the WM. (check the makers
spec for the model and see what the max pressure is. I would be
surprised if its going to be an issue)

but that we wouldn't be able to run hot water from two taps at the same time!

That depends entirely on the power of the combi you get. A small one
(24kW) will have difficulty delivering more than about 9 lpm in the
depths of winter. More powerful ones ( =35kW) will do much better. The
35kW one I had in my last place would do two concurrent showers with
"adequate" performance, or one with excellent performance.

This could be a worry if we couldn't wash our hands (or whatever) every time
the washing machine was filling or the other is running a bath. Can this
really be true?

What happens when a combi runs out of power to to heat the flow rate of
water being consumed, depends a little on the design. Some include rate
limiting that maintains the water at a reasonable temperature, but limit
the flow rate. Most will simply allow the temperature to fall, but carry
on delivering water at the rate requested.


Quote No. 1 includes an Ideal Logic+ 30kW boiler whilst No. 2 is for a
Worcester Bosch 15ri boiler. No. 1 includes quotes for both combi and non
combi options (but does give any indication of which non-combi boiler would
be fitted) and No. 2, as might be expected, doesn't have a second option!

How do these boilers compare - assume No. 1 would use a non-combi version of
the same boiler?

Internally combi boilers and "system" boilers [1] are very similar and
frequently share the same basic platform.

[1] a heating boiler that includes the pump, expansion vessel and most
of the components required to build a complete system in one box

All comments gratefully received!

Some background things to check. Is your mains flow rate adequate for a
combi? (you need a minimum of 15 lpm really, and more is better).

Is the pressure adequate. 3 bar or better is good.

Is the water supply reliable? (if not, some stored water may be handy).
Have you though about backup water heating if the boiler were in need of
repair?

If looking at stored water systems, have your installers been thinking
about using a conventional gravity fed cylinder, or an unvented one?
(the latter tend to give better overall system performance if there is
adequate mains flow rate availble)


--
Cheers,

John.

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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 20/05/2017 17:44, ChrisK wrote:

No issues with leakage from (now) pressurised 30 year old HW/CH system
(8mm microbore). This was my biggest worry as the water pressure round
here is highish (3 bar).

The mains water supply pressure has no real bearing on the primary
heating side of the boiler - that is pressurised via a filling loop to
typically a bit over 1 bar. It then rises somewhat as the water heats
up. The only bit of a the boiler that will see the full mains pressure
is the secondary heat exchanger that heats the water from the primary
side of the boiler.

There is a noticable issue with HW water flow rate upstairs &
interaction between showers & filling the bath is a bit slow. This is
probably down to re-using the original 15mm pipe work. It would have
been better to have replaced this with 22mm.

Choosing pipe sizes carefully can minimise interactions a bit. Although
a 15mm pipe will likely be able to supply as much hot water as most
combis can produce. Also a smaller pipe will give you less dead leg of
water to drawer off at each use.


--
Cheers,

John.

/================================================== ===============\
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|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

The Natural Philosopher wrote on 20/05/2017 :
work out how big a combi needs to be to say dump 400 litres a minute of water
at 60 degrees

then work out how much more expensive that is than a small boiler with a
mains pressure hot water tank

then do the sensible thng

For someone in at irregular times, where a timer cannot be set and who
doesn't mind waiting for the hot water to appear very slowly, they are
fine. For everyone else, who wants a bath filled rapidly, who might
need to run two taps at the same time - stored hot water.

On 20/05/2017 18:38, Scott wrote:
On Sat, 20 May 2017 13:35:45 +0100, Terry Casey
wrote:

[snip]

I installed a combi boiler (Worcester Bosch) last year and I am a bit
disappointed with it.

24kW by any chance?

(makes for dismal bath filling - but will do a "twice as good as the
best electric" shower)

The water takes a while to heat up when using Eco mode. I mostly run
without Eco mode (pre-heat is capable of being programmed) so I assume
I am using extra energy to save water.

Not much value in ECO mode really - it only fires fairly infrequently to
temper its small store of hot water.

The bath takes ages to fill. This may however be related to having an
unusual thermostatic mixer tap arrangement that serves the bath and
the shower.

Or an underpowered boiler...

The radiators warm up even when the heating is supposed to be off. I
understand this is because the boiler uses the heating as a heat sink
when it is pre-heating the hot water. Again, I assume this means
wasting energy.

That sounds more like a faulty diversion valve.

I find the extractor system noisy for a domestic application, but this
may be common to all condensing systems.

Extractor system?

(do you mean a fanned flue? If so, a standard feature of any boiler you
can buy today - although some are louder than others)

The hot water even at its maximum setting is not hot enough. It's
okay for filling sinks and baths in the first place but for a top-up
it is fairly ineffective.

The washing machine is cold fill so this is not an issue. I think
nearly all washing machines are cold fill, so probably your next one
will be. Could you not disable hot fill if this would help?

Depending on how well the plumbing is done you can get temperature
interactions even from cold fill only - especially of the WM cold feed
is taken from the pipe before the cold feed to the combi. Really it
wants to be plumbed with that being the first thing to be taken off from
the incoming main.


--
Cheers,

John.

/================================================== ===============\
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\================================================= ================/

On Sat, 20 May 2017 21:48:49 +0100, John Rumm
wrote:

On 20/05/2017 18:38, Scott wrote:
On Sat, 20 May 2017 13:35:45 +0100, Terry Casey
wrote:

[snip]

I installed a combi boiler (Worcester Bosch) last year and I am a bit
disappointed with it.

24kW by any chance?

Yes - I thought this would be okay for a flat.

(makes for dismal bath filling - but will do a "twice as good as the
best electric" shower)

Marvellous.

The water takes a while to heat up when using Eco mode. I mostly run
without Eco mode (pre-heat is capable of being programmed) so I assume
I am using extra energy to save water.

Not much value in ECO mode really - it only fires fairly infrequently to
temper its small store of hot water.

It does seem to make a big difference. Or at least if the heating is
on the water arrives more quickly. I may not be to do with Eco mode,
I suppose but I think it is as I think it is much the same effect even
if I turn the heating down to 10 degrees.

The bath takes ages to fill. This may however be related to having an
unusual thermostatic mixer tap arrangement that serves the bath and
the shower.

Or an underpowered boiler...

Or the hot water not nearly as hot as it was before?

The radiators warm up even when the heating is supposed to be off. I
understand this is because the boiler uses the heating as a heat sink
when it is pre-heating the hot water. Again, I assume this means
wasting energy.

That sounds more like a faulty diversion valve.

Is this what used to be called the 'motorised valve' when I was a boy?

I find the extractor system noisy for a domestic application, but this
may be common to all condensing systems.

Extractor system?

Flu gas extraction.

(do you mean a fanned flue? If so, a standard feature of any boiler you
can buy today - although some are louder than others)

Thought so, my neighbour's is even worse.

The hot water even at its maximum setting is not hot enough. It's
okay for filling sinks and baths in the first place but for a top-up
it is fairly ineffective.

The washing machine is cold fill so this is not an issue. I think
nearly all washing machines are cold fill, so probably your next one
will be. Could you not disable hot fill if this would help?

Depending on how well the plumbing is done you can get temperature
interactions even from cold fill only - especially of the WM cold feed
is taken from the pipe before the cold feed to the combi. Really it
wants to be plumbed with that being the first thing to be taken off from
the incoming main.

That's one for the OP. My washing machine is cold water (LG) for
which I am grateful given the unpredictable behaviour of the boiler.

As a complete diversion, if I wanted to replace my boiler with a mains
water filled storage tank is there a market for second-hand boilers or
would economic and regulatory issues consign it direct to the scrap
heap?

Scott has brought this to us :
That sounds more like a faulty diversion valve.

Is this what used to be called the 'motorised valve' when I was a boy?

Yes! You should be able to put a hand on the two outlet pipes and if
there is only call for one - HW or heating, only one should be hot.


Thought so, my neighbour's is even worse.

Our boiler is in a cupboard on the wall and is almost inaudible. I have
to open the door to hear if it is running.


That's one for the OP. My washing machine is cold water (LG) for
which I am grateful given the unpredictable behaviour of the boiler.

Quite easy to get a Y connector and feed cold to both hot and cold
inputs.



As a complete diversion, if I wanted to replace my boiler with a mains
water filled storage tank is there a market for second-hand boilers or
would economic and regulatory issues consign it direct to the scrap
heap?

There is no market for second hand boilers, much of the cost for most
people is the cost of installation. The might have some slight value to
a DIY installer.

In article ,
says...

Some background things to check. Is your mains flow rate adequate for a
combi? (you need a minimum of 15 lpm really, and more is better).

We are away at the moment but I will check it when we return in early June

Is the pressure adequate. 3 bar or better is good.

I have no way of checking this unless there is some simple method I could use

Is the water supply reliable? (if not, some stored water may be handy).
Have you though about backup water heating if the boiler were in need of
repair?

No supply problems in the year we've been there - although not all the time!

The electric shower heater should suffice for washing and the dishwasher and
washing machine would take care of most other essentials. The kettle will,
hopefully, cater for any more demand.

If looking at stored water systems, have your installers been thinking
about using a conventional gravity fed cylinder, or an unvented one?
(the latter tend to give better overall system performance if there is
adequate mains flow rate availble)

As the quote we are most interested in offers the option of a like for like
replacement instead of the combi, I was assuming that the cylinder would
remain gravity fed but will check.

--

Terry

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On 20/05/2017 21:20, Roger Mills wrote:


Firstly, do you bath or shower? Even a good combi will take a long time
to fill a bath with hot water compared with a stored hot water system.

You don't have to stand there and watch the bath fill up!


--
Adam

In article , says...

The first question is do you actually *need* a new boiler? What's wrong
with the existing system? There's no point in replacing it just because
it's "old" if it works ok and if spares are available. [My boiler is far
older than that - and still going strong - although I have updated the
controls.]


We've been discussing this and, whilst we haven't come to a decision yet, we
are thinking of just having the system flushed at the moment plus changing
one or two TRVs to see what the effect is.

We have been told that there is water being pumped into the header tank and
there is certainly a dripping noise when it is very quiet. My wife finds this
disturbing and can hear it if she has an early night before the heating turns
off and when it comes on again in the morning. If the system is flushed I'm
hoping the improved flow will get rid of this.

Another thing we've noticed is the number of times the boiler turns on for
a short period, then shuts down again when the heating is on which, again,
I'm assuming is caused by the restricted flow.

If you are convinced that you *do* need a new boiler, the choice between
conventional and combi depends on many factors.

Firstly, do you bath or shower? Even a good combi will take a long time
to fill a bath with hot water compared with a stored hot water system.

Bath in the bathroom and en suite electric shower

Are you desperate to get rid rid of your hot water cylinder in order to
redeploy the space for some other purpose?

There is very limited easily accessible storage room and my wife would love
to regain the space that the cylinder takes up in the airing cupboard!

Have you got decent pressure and flow from your cold water mains. I
think the figure often quoted is that the mains needs to be able to
deliver at least 14 litres per minute at the point of entry - often the
kitchen tap.

I will check this when we return next month

Is your gas pipework up to the job. A combi will consume gas at a very
high rate when heating the hot water (as opposed to the radiators) so
the internal gas pipework may need upgrading.

Improving gas flow included in combi quote


--

Terry

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Andrew wrote:
On 20/05/2017 17:44, ChrisK wrote:
There is a noticable issue with HW water flow rate upstairs &
interaction between showers & filling the bath is a bit slow. This is
probably down to re-using the original 15mm pipe work. It would have
been better to have replaced this with 22mm.

If your mains pressure and flow rate are adequate then 15mm should be
fine. Sounds like you have another problem somewhere.

Probably not, it is quite a tortuous route the 15mm feed follows to join
the upstairs HW pipework which is all 22mm. Not bad enough to do
anything about it as it would involve taking up a lot of flooring.

CK

John Rumm wrote:
On 20/05/2017 17:44, ChrisK wrote:

The mains water supply pressure has no real bearing on the primary
heating side of the boiler - that is pressurised via a filling loop to
typically a bit over 1 bar. It then rises somewhat as the water heats
up. The only bit of a the boiler that will see the full mains pressure
is the secondary heat exchanger that heats the water from the primary
side of the boiler.


Of course, I knew that :-(, must engage brain before touching
keyboard... It is running at about 1.5 bar.

There is a noticable issue with HW water flow rate upstairs &
interaction between showers & filling the bath is a bit slow. This is
probably down to re-using the original 15mm pipe work. It would have
been better to have replaced this with 22mm.

Choosing pipe sizes carefully can minimise interactions a bit. Although
a 15mm pipe will likely be able to supply as much hot water as most
combis can produce. Also a smaller pipe will give you less dead leg of
water to drawer off at each use.



Agree, it's not a problem, just a noticeable side effect & the 15mm pipe
run is quite long with a lot of bends in it.

CK

A system boiler of 8-15kW, plus pressurised hot water tank with the
added advantage of an immersion heater if you don't want to run the
boiler, is around £1200 in total.

A 45Kw combi to deliver the same hot water flow rate is similar, or more
costly, and is certainly bigger in the boiler room

(You can site a pressurised cylinder wherever you like)

If you have an unpressurised tank you need pumped showers.

(Interestingly, in the two new builds going up here, with no mains gas,
they are using air source heat pumps, UFH, and a pressurised tank plus
the mandatory immersion heater to bring the stored temp up to 60C to
kill the bugs. Air sourced heat pumps simply can't deliver the peak
output, and indeed the insulation level installed to allow them to even
heat the house at all is phenomenal)

To heat 15 l/min (an average single shower) from 5C to say 45C takes 42KW.

To fill a bath with water at 45C in 4 minutes is around 20l/min or 55KW.

For sure you can add a heat store to a combi at EVEN MORE EXPENSE to
give better figures than this, but that is pretty much what a DPHW
system IS.

My point is simple. Heating a house requires a constant low to medium
heat output over a long period of time. A boiler designed to do that
efficiently does not have the capability for a massive output over 4
minutes of the day when you want to fill a bath. Attempts to rectify
this with high power but modulating boilers etc simply make the boiler
more complex and costly.

The simplest solution is a heat store. Mutatis mutandis a decent sized
heatbank on a combi is no different to a system boiler with a DPHW tank
attached.

The more complex solution is a thwacking great boiler.

Prices are similar, but even then, if you install the monster combi, you
can STILL only cope with one shower or bath at a time and you cannot
open a hot tap elsewhere.


The worst solution is to enforce a pathetic rate of hot water flow on
the house-owner. Because you didn't give a **** when you built the poxy
little house you sold him.

Actually no, the worst solution is a gravity fed unpressurised tank. In
a bedroom, so no upstairs hot water pressure exists at all, and you have
to pump.

In short:

Installing a system boiler geared to the CH requirements and a DPHW tank
to provide peak flow of piping hot water gets you the optimal solution
to both problems, and is no more expensive than a small combi with a
large heat bank, or a large combi with no heat bank.


And even a large combi can't meet the same peak demands that stored hot
water can.

The only cheap option is a pathetically limited small combi with litle
or no heat bank.

Or a gravity fed cheap water tank with a system boiler.

I have experienced both. They suck, big time,.


--
Ideas are more powerful than guns. We would not let our enemies have
guns, why should we let them have ideas?

Josef Stalin

On 21/05/2017 09:41, Scott wrote:
On Sat, 20 May 2017 21:48:49 +0100, John Rumm

Not much value in ECO mode really - it only fires fairly infrequently to
temper its small store of hot water.

It does seem to make a big difference. Or at least if the heating is
on the water arrives more quickly.

Yup, having eco mode turned off makes it far more usable IME - with
faster hot water delivery, especially when all you want is a small
amount. Eco mode on will save some gas, but I would not expect it to
make a significant difference to consumption in most households.

I may not be to do with Eco mode,
I suppose but I think it is as I think it is much the same effect even
if I turn the heating down to 10 degrees.

The bath takes ages to fill. This may however be related to having an
unusual thermostatic mixer tap arrangement that serves the bath and
the shower.

Or an underpowered boiler...

Or the hot water not nearly as hot as it was before?

Often with combi you won't be adding any cold to the mix - i.e. you
select a fill rate that delivers the hot water at final use temperature.
When that is the case, the boiler is running flat out anyway.

Unlike a stored water system, you don't have the option to deliver the
hot water at a much higher temperature than you need so that you can
augment it with extra cold water (or at least there is no advantage in
doing so, since to get it hotter, you need to have it slower).

Its sometimes instructive to do the sums for various inlet and outlet
temperatures to see what rates you can expect. If you assume that a kg
of water needs 4200 joules of energy for every C lift in temperature,
and the combi can provide 24000 x 60 joules per minute, then you can get
some numbers. So for example, if the incoming water is at 10 deg C, and
you want a bath at 45 deg C, then that's a 35 degree lift. 24000 x 60 /
35 / 4200 = just under 10 lpm. If the inlet water is colder, say 5 deg,
and you want water at 50, then it becomes 24000 x 60 / 45 / 4200 = bit
over 7.5 lpm.

The radiators warm up even when the heating is supposed to be off. I
understand this is because the boiler uses the heating as a heat sink
when it is pre-heating the hot water. Again, I assume this means
wasting energy.

That sounds more like a faulty diversion valve.

Is this what used to be called the 'motorised valve' when I was a boy?

Yup mostly. Depending on the boiler it might be motorised, or some have
a kind of solenoid activated one. However the basic principle is common
to many combis; when they detect DHW flow, they fire up the main burner,
and activate the diversion valve. This re-routes the primary flow so
that it only goes through the secondary plate heat exchanger for the hot
water and not the rads. If this valve were not fully diverting the flow,
then you would expect the rads to get warm, and the ability to heat the
incoming cold water would be impaired.

As a complete diversion, if I wanted to replace my boiler with a mains
water filled storage tank is there a market for second-hand boilers or
would economic and regulatory issues consign it direct to the scrap
heap?

The latter usually alas, unless you can flog it to someone who will self
install.

Note however, that you *can* have a hot water cylinder heated with a
combi. Just because it can also do hot water on its own, does not mean
you have to use that capability. There is nothing stopping you from
adding external zone valves and controls to divert the CH water through
a cylinder in the normal way.

In some cases this can be a system worth installing from new. if you
have a conventional gravity fed HW cylinder. You get fast bath filling,
but also have mains pressure (wholesome) hot water available direct from
the combi side for either a shower or kitchen tap. With a mains (i.e.
unvented) cylinder, then there is less benefit in this approach since
the cylinder will also feed a good shower. However if you already have
the boiler, it saves the cost of replacing that - and 24kW is more than
adequate for a fast cylinder recharge.




--
Cheers,

John.

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