Hello,

I have moved into a house with an old non-condensing combi boiler.

I am thinking of replacing it before the winter but I am unsure what
to replace it with. There is a loft conversion with an en suite, so my
first thought was that there was no room for a header tank for a
non-combi boiler. However there is some space above the plasterboard
ceiling in the apex of the loft conversion and the joists look a
decent thickness, so it is possible that I could fit a header tank up
there.

The advantage of a combi boiler is that I would only heat what I need
but the disadvantage would be no immersion heater in a cylinder as a
back-up if the boiler failed.

My last house had gravity fed HW in 22mm pipe and I feel that the bath
filled much more quickly there. I like baths and I find that in the
new house it takes at least 10 minutes to run the bath. The bath is
plumbed in 15mm pipe. Is this normal with combi boilers? Is it that
because the water is at mains pressure rather than gravity fed, a
smaller pipe diameter can be used? Would I see no benefit from using
22mm pipe?

I find the combi boiler pretty useless for washing my hands. If I turn
on the tap in the kitchen, I can hear the fan start but the gas has
not ignited before I switch the tap off. Are all combi boilers this
slow to light?

If I go down the route of replacing the combi with another combi, what
flow rate figures should I look for to ensure a quick filling bath or
a decent shower?

What are these ERP ratings that manufacturers are quoting?

The old boiler is under the stairs. Is this still allowed? I thought
you had to have a 30 minute barrier if you installed there?

What about micro CHP boiler. I presume it is much more expensive? Has
anyone got one?

Thanks,
Stephen.

On 30/06/2015 08:45, Stephen wrote:
Hello,

I have moved into a house with an old non-condensing combi boiler.

I am thinking of replacing it before the winter but I am unsure what
to replace it with. There is a loft conversion with an en suite, so my
first thought was that there was no room for a header tank for a
non-combi boiler. However there is some space above the plasterboard
ceiling in the apex of the loft conversion and the joists look a
decent thickness, so it is possible that I could fit a header tank up
there.

The advantage of a combi boiler is that I would only heat what I need
but the disadvantage would be no immersion heater in a cylinder as a
back-up if the boiler failed.


Electric shower?

My last house had gravity fed HW in 22mm pipe and I feel that the bath
filled much more quickly there. I like baths and I find that in the
new house it takes at least 10 minutes to run the bath. The bath is
plumbed in 15mm pipe. Is this normal with combi boilers? Is it that
because the water is at mains pressure rather than gravity fed, a
smaller pipe diameter can be used? Would I see no benefit from using
22mm pipe?

I find the combi boiler pretty useless for washing my hands. If I turn
on the tap in the kitchen, I can hear the fan start but the gas has
not ignited before I switch the tap off. Are all combi boilers this
slow to light?


Mine lights within a second or two, but takes a good 10s to feed hot
water. Complete waste - so much for 'efficiency'.



--
Cheers, Rob

On Tuesday, June 30, 2015 at 8:45:47 AM UTC+1, Stephen wrote:
Hello,

I have moved into a house with an old non-condensing combi boiler.

I am thinking of replacing it before the winter but I am unsure what
to replace it with. There is a loft conversion with an en suite, so my
first thought was that there was no room for a header tank for a
non-combi boiler. However there is some space above the plasterboard
ceiling in the apex of the loft conversion and the joists look a
decent thickness, so it is possible that I could fit a header tank up
there.

If it works fine, does it need replacing? Is the extra efficiency of a condensing boiler worth throwing away the existing one? And do you have radiator sizings such that the new boiler will actually run in condensing mode?

Be very careful about putting a tank up there. Joists may look strong but don't underestimate the weight of a water tank.


The advantage of a combi boiler is that I would only heat what I need
but the disadvantage would be no immersion heater in a cylinder as a
back-up if the boiler failed.

My last house had gravity fed HW in 22mm pipe and I feel that the bath
filled much more quickly there. I like baths and I find that in the
new house it takes at least 10 minutes to run the bath. The bath is
plumbed in 15mm pipe. Is this normal with combi boilers? Is it that
because the water is at mains pressure rather than gravity fed, a
smaller pipe diameter can be used? Would I see no benefit from using
22mm pipe?

Wide pipe is used to get sufficient flow from a low pressure system (gravity). With combis the pressure is not the problem, so 15mm is fine.
Regarding filling a bath, just get it going and do something else for 10 minutes.


I find the combi boiler pretty useless for washing my hands. If I turn
on the tap in the kitchen, I can hear the fan start but the gas has
not ignited before I switch the tap off. Are all combi boilers this
slow to light?

Mine is a bit faster than that. You can also get combis that include a small water tank to tide you over until the direct heated water is up to temperature. Another common setting is a "stay warm" function where the heat exchanger is kept warm by periodic boiler firings, so the hot water comes sooner.

On Tue, 30 Jun 2015 08:45:43 +0100, Stephen wrote:
snip
The advantage of a combi boiler is that I would only heat what I need
but the disadvantage would be no immersion heater in a cylinder as a
back-up if the boiler failed.

My last house had gravity fed HW in 22mm pipe and I feel that the bath
filled much more quickly there. I like baths and I find that in the new
house it takes at least 10 minutes to run the bath. The bath is plumbed
in 15mm pipe. Is this normal with combi boilers? Is it that because the
water is at mains pressure rather than gravity fed, a smaller pipe
diameter can be used? Would I see no benefit from using 22mm pipe?

I find the combi boiler pretty useless for washing my hands. If I turn
on the tap in the kitchen, I can hear the fan start but the gas has not
ignited before I switch the tap off. Are all combi boilers this slow to
light?
snip

This is probably the length of the pipe run from the boiler to the tap - I
had a stored water system with a long pipe run and it took ages for the
hot water to get to the tap.

Flow rates from combis are bound to be slower than gravity fed through
large bore pipe - there is a limit to how much heat you can get into water
that is charging past. Limited by not just the boiler but the gas supply
as well.

I now have a combi, but the best system I have had is a large hot water
tank and header tank with a power shower pump.

Glorious showers, and it also filled the bath very quickly!

Cheers

Dave R

--
Windows 8.1 on PCSpecialist box

On 30/06/2015 08:45, Stephen wrote:
Hello,

I have moved into a house with an old non-condensing combi boiler.

I am thinking of replacing it before the winter but I am unsure what
to replace it with. There is a loft conversion with an en suite, so my
first thought was that there was no room for a header tank for a
non-combi boiler. However there is some space above the plasterboard

You are confusing combi boiler (i.e. one that heats hot water on demand
as well as running the CH) with a sealed system boiler. The two are
unrelated. Most combis use a sealed system (no header tank) but not all.
Other boiler types are also available in bot sealed and vented forms.

ceiling in the apex of the loft conversion and the joists look a
decent thickness, so it is possible that I could fit a header tank up
there.

Why would you want one?

The advantage of a combi boiler is that I would only heat what I need
but the disadvantage would be no immersion heater in a cylinder as a
back-up if the boiler failed.

and your flow rate of hot water will be limited by the power of the
boiler...

My last house had gravity fed HW in 22mm pipe and I feel that the bath
filled much more quickly there. I like baths and I find that in the
new house it takes at least 10 minutes to run the bath. The bath is
plumbed in 15mm pipe. Is this normal with combi boilers?

Yes, most are not powerful enough to need a larger pipe size. Plus they
run at higher pressure and so its less of an issue.

Is it that
because the water is at mains pressure rather than gravity fed, a
smaller pipe diameter can be used?

Yup, that and also the fact that even a 35kW combi can only manage 15
lpm of water at final temperature in the winter - and that will not be a
problem with 15mm pipe.

Would I see no benefit from using
22mm pipe?

No, you would just experience more delay for the hot water to come through.

I find the combi boiler pretty useless for washing my hands. If I turn
on the tap in the kitchen, I can hear the fan start but the gas has
not ignited before I switch the tap off. Are all combi boilers this
slow to light?

Some keep a small store of preheated water so as to minimise the delay
in production.

If I go down the route of replacing the combi with another combi, what
flow rate figures should I look for to ensure a quick filling bath or
a decent shower?

35kW as a minimum. In reality you will never match a stored water system
for flow rate - some of which will deliver at a rate that a combi could
only manage with an output of 100kW. Since you gas meter is not rated
for even half that, its a non starter.

What are these ERP ratings that manufacturers are quoting?

pass

The old boiler is under the stairs. Is this still allowed? I thought
you had to have a 30 minute barrier if you installed there?

Its still allowed. Although you will need a route for the condensate
drain with a new boiler.

What about micro CHP boiler. I presume it is much more expensive? Has
anyone got one?

I am not sure I really see the logic of these (other than the normal
reason of attempting to extract incentives and paybacks from various
daft government schemes). All they do is divert some electricity
generation from a highly efficient combined cycle gas turbine power
station to a less efficient single cycle boiler.

Other options to consider if you have space, would be either a heatbank
or an unvented cylinder. Both can give high flow rates, immersion backup
and mains pressure delivery with no need for header tanks.

See:

http://wiki.diyfaq.org.uk/index.php?...and_Heat_Banks

and

http://wiki.diyfaq.org.uk/index.php?title=Unvented_DHW


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Tue, 30 Jun 2015 15:34:28 +0100, John Rumm wrote:

On 30/06/2015 08:45, Stephen wrote:
Hello,

I have moved into a house with an old non-condensing combi boiler.

I am thinking of replacing it before the winter but I am unsure what to
replace it with. There is a loft conversion with an en suite, so my
first thought was that there was no room for a header tank for a
non-combi boiler. However there is some space above the plasterboard

You are confusing combi boiler (i.e. one that heats hot water on demand
as well as running the CH) with a sealed system boiler. The two are
unrelated. Most combis use a sealed system (no header tank) but not all.
Other boiler types are also available in bot sealed and vented forms.

ceiling in the apex of the loft conversion and the joists look a decent
thickness, so it is possible that I could fit a header tank up there.

Why would you want one?

The advantage of a combi boiler is that I would only heat what I need
but the disadvantage would be no immersion heater in a cylinder as a
back-up if the boiler failed.

and your flow rate of hot water will be limited by the power of the
boiler...

My last house had gravity fed HW in 22mm pipe and I feel that the bath
filled much more quickly there. I like baths and I find that in the new
house it takes at least 10 minutes to run the bath. The bath is plumbed
in 15mm pipe. Is this normal with combi boilers?

Yes, most are not powerful enough to need a larger pipe size. Plus they
run at higher pressure and so its less of an issue.

Is it that because the water is at mains pressure rather than gravity
fed, a smaller pipe diameter can be used?

Yup, that and also the fact that even a 35kW combi can only manage 15
lpm of water at final temperature in the winter - and that will not be a
problem with 15mm pipe.

Would I see no benefit from using 22mm pipe?

No, you would just experience more delay for the hot water to come
through.

I find the combi boiler pretty useless for washing my hands. If I turn
on the tap in the kitchen, I can hear the fan start but the gas has not
ignited before I switch the tap off. Are all combi boilers this slow to
light?

Some keep a small store of preheated water so as to minimise the delay
in production.

If I go down the route of replacing the combi with another combi, what
flow rate figures should I look for to ensure a quick filling bath or a
decent shower?

35kW as a minimum. In reality you will never match a stored water system
for flow rate - some of which will deliver at a rate that a combi could
only manage with an output of 100kW. Since you gas meter is not rated
for even half that, its a non starter.

What are these ERP ratings that manufacturers are quoting?

pass

The old boiler is under the stairs. Is this still allowed? I thought
you had to have a 30 minute barrier if you installed there?

Its still allowed. Although you will need a route for the condensate
drain with a new boiler.

What about micro CHP boiler. I presume it is much more expensive? Has
anyone got one?

I am not sure I really see the logic of these (other than the normal
reason of attempting to extract incentives and paybacks from various
daft government schemes). All they do is divert some electricity
generation from a highly efficient combined cycle gas turbine power
station to a less efficient single cycle boiler.

Other options to consider if you have space, would be either a heatbank
or an unvented cylinder. Both can give high flow rates, immersion backup
and mains pressure delivery with no need for header tanks.

See:

http://wiki.diyfaq.org.uk/index.php?...and_Heat_Banks

and

http://wiki.diyfaq.org.uk/index.php?title=Unvented_DHW

Just to add to John's excellent list, AFAIK without a header tank or other
cold water storage method you are ultimately limited to the maximum flow
rate of your mains water supply to supply both hot and cold to your bath.

I remember that I could empty the large loft tank after a while if running
both showers off the shower pump. The flow rate was far higher than the
maximum flow in from the mains.

So you need to have some idea of the maximum delivery of cold water to the
house before you can be sure that you can fill your bath in the time
desired.

Cheers

Dave R





--
Windows 8.1 on PCSpecialist box

On Tue, 30 Jun 2015 15:34:28 +0100, John Rumm
wrote:

Yup, that and also the fact that even a 35kW combi can only manage 15
lpm of water at final temperature in the winter - and that will not be a
problem with 15mm pipe.

So if I redo some plumbing if I want to have the new boiler in a
different location, I can just run one 15mm pipe and tee off to the
bathroom, kitchen, etc. It won't be a problem even if all taps are
open at once?

In message , Stephen
writes
On Tue, 30 Jun 2015 15:34:28 +0100, John Rumm
wrote:

Yup, that and also the fact that even a 35kW combi can only manage 15
lpm of water at final temperature in the winter - and that will not be a
problem with 15mm pipe.

So if I redo some plumbing if I want to have the new boiler in a
different location, I can just run one 15mm pipe and tee off to the
bathroom, kitchen, etc. It won't be a problem even if all taps are
open at once?

John meant, that 15mm pipe won't have a problem delivering 15 lpm of HW.

It will still be a problem in that if you have a big draw - filling the
bath or having a shower, then turning on say the kitchen tap will reduce
the flow to the bath or whatever.

But that will happen however you arrange the plumbing. All the HW water
has to come from the boiler and that is the limiting factor.

You should get a decent shower from a combi, but filling a bath is
always going to be slow
--
Chris French

On 03/07/2015 12:07, Stephen wrote:
On Tue, 30 Jun 2015 15:34:28 +0100, John Rumm
wrote:

Yup, that and also the fact that even a 35kW combi can only manage 15
lpm of water at final temperature in the winter - and that will not be a
problem with 15mm pipe.

So if I redo some plumbing if I want to have the new boiler in a
different location, I can just run one 15mm pipe and tee off to the
bathroom, kitchen, etc. It won't be a problem even if all taps are
open at once?

Once you are drawing whatever flow rate the combi can heat adequately,
trying to take more will (depending on the combi, and whether it has
flow regulation or not) either get you more cooler water or the same
amount of water shared between the taps.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 03/07/2015 16:03, Chris French wrote:
In message , Stephen
writes
On Tue, 30 Jun 2015 15:34:28 +0100, John Rumm
wrote:

Yup, that and also the fact that even a 35kW combi can only manage 15
lpm of water at final temperature in the winter - and that will not be a
problem with 15mm pipe.

So if I redo some plumbing if I want to have the new boiler in a
different location, I can just run one 15mm pipe and tee off to the
bathroom, kitchen, etc. It won't be a problem even if all taps are
open at once?

John meant, that 15mm pipe won't have a problem delivering 15 lpm of HW.

It will still be a problem in that if you have a big draw - filling the
bath or having a shower, then turning on say the kitchen tap will reduce
the flow to the bath or whatever.

But that will happen however you arrange the plumbing. All the HW water
has to come from the boiler and that is the limiting factor.

You should get a decent shower from a combi, but filling a bath is
always going to be slow

Keep in mind there is nothing to stop you using a combi to heat a
traditional vented cylinder as well as having its own supply of hot
water. Some may do that to have good bath filling performance, but also
mains pressure hot water direct from the combi either for a shower, or a
short dead leg to a particular tap etc.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/