"Andy Hall" wrote in message
...
On Tue, 27 Dec 2005 23:09:08 -0000, "Doctor Drivel"
wrote:



The Highflow is NOT a CPSU.

Just seeing if you were awake.....

Sure you were.

"raden" wrote in message
...
In message .uk, Ed
Sirett writes
On Tue, 27 Dec 2005 10:23:39 +0000, Andy Hall wrote:

On Tue, 27 Dec 2005 10:16:36 -0000, "Doctor Drivel"
wrote:


"Ed Sirett" wrote in message
newsan.2005.12.27.00.06.19.787075@makewrite. demon.co.uk...
On Mon, 26 Dec 2005 18:52:23 +0000, Nick wrote:

Hi Ed,

I was wondering if you had seen any / many
Wickes Combis, the 102,000 btu item ?
It is a Halstead, possibly the Ace High,
with a Wickes badge ?

The sheds and catalogues (Screwfux
and TollStation etc.) tend to rebadge
low end boilers to be sold on price.

I really must write the how to choose a boiler FAQ.

Please don't has you clearly don't know too much about them. 10
litre/min
from wall hung combis? Please. The FAQ needs to have correct and
factual
information, nothing that is misleading, no old wives tales or personal
prejudices.


So you won't be contributing then?

I'm about half way through. I'll willingly take into consideration
everyones comments. I'm quite pleased with the generosity of the good
doctor's offer to edit it. ISTR that when he looked at the Sealed CH FAQ
he only got to the first paragraph before giving up and declaring the
work as 'incomplete' and 'wrong'.

What did you expect ?

Maxie, if it is wrong it is wrong. Season's greetings to you Maxie. Just to
think, you have another boozing session in a few days time.

On Wed, 28 Dec 2005 12:00:24 -0000, "Doctor Drivel"
wrote:


"Andy Hall" wrote in message
.. .
On Tue, 27 Dec 2005 23:09:08 -0000, "Doctor Drivel"
wrote:



The Highflow is NOT a CPSU.

Just seeing if you were awake.....

Sure you were.

Proven. It's taken you this long to reply.

FWIW
According to SEDBUK, a CPSU is defined by having a store at high
temperature (80 degrees or so), with capacity of 70 litres or more and
which also feeds the heating circuit as well as providing primary
water to be pumped through the heat exchanger for the DHW.

In essence, a mini heatbank and boiler in a box.

The Heatflow also has a store heated to high temperature providing
primary water to be pumped through the DHW heat exchanger. The size
is not mentioned by the manufacturer, but judging by the manual, is
less than 70 litres. The store is not used to supply the heating
circuit.

In terms of the way that the DHW is heated, the principle is the same
- it is a matter of scale, and of course the 70 litre store size is an
arbitrary number used to establish a definition.


--

..andy

"Andy Hall" akak Matt wrote in message
...

The Highflow is NOT a CPSU.

Just seeing if you were awake.....

Sure you were.

Proven. It's taken you this long to reply.

FWIW
According to SEDBUK, a CPSU is
defined by having a store at high
temperature (80 degrees or so), with
capacity of 70 litres or more and
which also feeds the heating circuit
as well as providing primary
water to be pumped through the heat
exchanger for the DHW.

In essence, a mini heatbank and boiler in a box.

Yep Matt.

The Heatflow also has a store heated
to high temperature providing
primary water to be pumped through
the DHW heat exchanger. The size
is not mentioned by the manufacturer,
but judging by the manual, is
less than 70 litres. The store is not
used to supply the heating circuit.

Matt, so not a CPSU.

In terms of the way that the DHW
is heated, the principle is the same

But Matt....a CPSU has the DHW & CH taken off the store of water and the
boiler "only" heats the store eliminating boiler cycling. So the Heatflow
is not a CPSU.

The ACV Heatmaster is a hybrid of thermal store and unvented cylinder
(although to complicate matters the unvented cylinder can be vented by
removing the pressure controls). The CH is taken directly off the store of
water and DHW via an unvented cylinder immersed in the store of water heated
by the store of water. So, in effect a CPSU, but SEDUK don't think so.

- it is a matter of scale, and of course
the 70 litre store size is an
arbitrary number used to establish
a definition.

On Wed, 28 Dec 2005 14:52:55 -0000, "Doctor Drivel"
wrote:



But Matt....a CPSU has the DHW & CH taken off the store of water and the
boiler "only" heats the store eliminating boiler cycling. So the Heatflow
is not a CPSU.

If you think about it, since it's a modulating boiler, it won't cycle
at any great rate when driving only the heating circuit anyway.



The ACV Heatmaster is a hybrid of thermal store and unvented cylinder
(although to complicate matters the unvented cylinder can be vented by
removing the pressure controls). The CH is taken directly off the store of
water and DHW via an unvented cylinder immersed in the store of water heated
by the store of water. So, in effect a CPSU, but SEDUK don't think so.

Which demonstrates that the definition is arbitrary, doesn't it.



- it is a matter of scale, and of course
the 70 litre store size is an
arbitrary number used to establish
a definition.

--

..andy

"Andy Hall" aka Matt wrote in message
news
On Wed, 28 Dec 2005 14:52:55 -0000, "Doctor Drivel"
wrote:

But Matt....a CPSU has the DHW &
CH taken off the store of water and the
boiler "only" heats the store eliminating
boiler cycling. So the Heatflow
is not a CPSU.

If you think about it, since it's a
modulating boiler, it won't cycle
at any great rate when driving only
the heating circuit anyway.

Matt, the CH 'and' the DHW have to be taken off the store.

The ACV Heatmaster is a hybrid of
thermal store and unvented cylinder
(although to complicate matters the
unvented cylinder can be vented by
removing the pressure controls). The
CH is taken directly off the store of
water and DHW via an unvented
cylinder immersed in the store of
water heated by the store of water.
So, in effect a CPSU, but SEDUK don't think so.

Which demonstrates that the
definition is arbitrary, doesn't it.

No it isn't. Sedbuk got it wrong. An immersed DHW coil or immersed DHW
cylinder are basically the same thing in this context. Both dipped inside a
thermal store.

On Wed, 28 Dec 2005 15:55:17 -0000, "Doctor Drivel"
wrote:


"Andy Hall" aka Matt wrote in message
news
On Wed, 28 Dec 2005 14:52:55 -0000, "Doctor Drivel"
wrote:

But Matt....a CPSU has the DHW &
CH taken off the store of water and the
boiler "only" heats the store eliminating
boiler cycling. So the Heatflow
is not a CPSU.

If you think about it, since it's a
modulating boiler, it won't cycle
at any great rate when driving only
the heating circuit anyway.

Matt, the CH 'and' the DHW have to be taken off the store.

They don't *have* to be. This is just something that is implemented
on that type of appliance.



The ACV Heatmaster is a hybrid of
thermal store and unvented cylinder
(although to complicate matters the
unvented cylinder can be vented by
removing the pressure controls). The
CH is taken directly off the store of
water and DHW via an unvented
cylinder immersed in the store of
water heated by the store of water.
So, in effect a CPSU, but SEDUK don't think so.

Which demonstrates that the
definition is arbitrary, doesn't it.

No it isn't. Sedbuk got it wrong.

Oh of course, silly me. Which manufacturer's web site got it "right"

An immersed DHW coil or immersed DHW
cylinder are basically the same thing in this context. Both dipped inside a
thermal store.


--

..andy

"Andy Hall" aka Matt wrote in message
...
On Wed, 28 Dec 2005 15:55:17 -0000, "Doctor Drivel"
wrote:

"Andy Hall" aka Matt wrote in message
news
On Wed, 28 Dec 2005 14:52:55 -0000, "Doctor Drivel"
wrote:

But Matt....a CPSU has the DHW &
CH 'taken off the store of water' and the
boiler "only" heats the store eliminating
boiler cycling. So the Heatflow
is not a CPSU.

If you think about it, since it's a
modulating boiler, it won't cycle
at any great rate when driving only
the heating circuit anyway.

Matt, the CH 'and' the DHW have to be taken off the store.

They don't *have* to be.

Matt, to be a CPSU they have to.

The ACV Heatmaster is a hybrid of
thermal store and unvented cylinder
(although to complicate matters the
unvented cylinder can be vented by
removing the pressure controls). The
CH is taken directly off the store of
water and DHW via an unvented
cylinder immersed in the store of
water heated by the store of water.
So, in effect a CPSU, but SEDUK don't think so.

Which demonstrates that the
definition is arbitrary, doesn't it.

No it isn't. Sedbuk got it wrong.

Oh of course, silly me.

Matt, self awareness, encouraging.

danw wrote:
I'm seeking advice.

We're currently looking to replace our system boiler and hot water tank.
The boiler and tank are too small for our house (detached, 30s, 3 beds,
one bath, 3 downstairs rooms with small kitchen extension).

We've had a couple of heating engineers in and are receiving conflicting
advice; as I am sure I will get here!

First chap said that a combi would be no good for our house. He said he
would never use them and that they are no good for a house of our size.
He also said that we would need to replace our old iron gas supply, even
though it appears to be large enough.

Second man said that a combi would be fine, he recommended a
floor-standing, Worcester Greenflow. Said we wouldn't need to replace
the gas supply it would be fine. Said a wall mounted boiler would not be
big enough. Having a floor standing boiler is less than ideal as it
would take up much needed floor space in our small kitchen.

Third man says we would be fine with a wall mounted combi but said we'd
need a new gas supply as old iron pipes a likely to rust and this can
get inside the boiler. He also said they are prone to cracking and leaking.

What we would ideally like is: a combi, wall-mounted, with no new gas
supply if possible. We are a small family (2 little kids), with not a
lot of spare cash, and not a lot of room in our kitchen for the boiler.

I know that, ultimately, the decision is ours but if anyone has any
advice for us it would be much appreciated.

thanks in advance, dan

Dan ignore all conflicting advice and go for a combi. It never ceases
to amaze me that English people love to store hot water in poorly
lagged hot water tanks. This is unheard of on the continent. Combi's
are easier to install, there is no hot water storage tank and no header
tank in the loft. A lot less pipe work and also fewer electricity
cables. I have a big combi boiler 102,000 btu (should heat half the
street) heating an antiquated micro-bore system (should be banned by
law). It's my second combi boiler and is the business. I installed a
conventional boiler for my mother several years ago and have regreted
it ever since.

Why don't you install the boiler (combi) yourself? If you did mechano
as a child it should be child's play! Try to ignore the technical data
it's for technical nerds only! Never be blinded by science I say.

Oh and wall mounted boilers are smaller than floor-standing boilers but
you might need help hoisting them onto the wall because they are heavy.
The new condensing boilers are very efficient.

Regards Alan from Exeter

"alanjones" wrote in message
oups.com...

Dan ignore all conflicting advice
and go for a combi.

I agree.

It never ceases to amaze me that
English people love to store hot water in poorly
lagged hot water tanks.

I am amazed too.

This is unheard of on the continent. Combi's
are easier to install, there is no hot water
storage tank and no header
tank in the loft.

The UK and Ireland are alone in this setup.

A lot less pipe work and also fewer electricity
cables. I have a big combi boiler 102,000 btu

That is not big.

(should heat half the street)

Not in DHW it will not.

heating an antiquated micro-bore
system (should be banned by
law).

For what inexplicable reason?

It's my second combi boiler and
is the business. I installed a
conventional boiler for my
mother several years ago and have regreted
it ever since.

Why don't you install the boiler (combi)
yourself? If you did mechano
as a child it should be child's play!
Try to ignore the technical data
it's for technical nerds only! Never
be blinded by science I say.

Oh and wall mounted boilers are
smaller than floor-standing boilers but
you might need help hoisting them onto
the wall because they are heavy.
The new condensing boilers are very efficient.

Regards Alan from Exeter

"danw" wrote in message
...
I'm seeking advice.

We're currently looking to replace our system boiler and hot water tank.
The boiler and tank are too small for our house (detached, 30s, 3 beds,
one bath, 3 downstairs rooms with small kitchen extension).

We've had a couple of heating engineers in and are receiving conflicting
advice; as I am sure I will get here!

First chap said that a combi would be no good for our house. He said he
would never use them and that they are no good for a house of our size. He
also said that we would need to replace our old iron gas supply, even
though it appears to be large enough.

Second man said that a combi would be fine, he recommended a
floor-standing, Worcester Greenflow. Said we wouldn't need to replace the
gas supply it would be fine. Said a wall mounted boiler would not be big
enough. Having a floor standing boiler is less than ideal as it would take
up much needed floor space in our small kitchen.

Third man says we would be fine with a wall mounted combi but said we'd
need a new gas supply as old iron pipes a likely to rust and this can get
inside the boiler. He also said they are prone to cracking and leaking.

What we would ideally like is: a combi, wall-mounted, with no new gas
supply if possible. We are a small family (2 little kids), with not a lot
of spare cash, and not a lot of room in our kitchen for the boiler.

I know that, ultimately, the decision is ours but if anyone has any advice
for us it would be much appreciated.

thanks in advance, dan

I saw a great set-up the other day...

Unvented cylinder, heated via solar panels (actually evacuated tubes), which
then passed through a Worcester condensing boiler for DHW. The boiler
simply topped up any heat demand required. The cylinder sat at 25c even in
the winter, therefore using a lot less energy to satisfy demand. Also had
an immersion in case of boiler problems.

Probably not that rare - first one I've seen though.

Angus

On Tue, 27 Dec 2005 23:38:11 +0000, raden wrote:

In message .uk, Ed
Sirett writes
On Tue, 27 Dec 2005 10:23:39 +0000, Andy Hall wrote:

On Tue, 27 Dec 2005 10:16:36 -0000, "Doctor Drivel"
wrote:


"Ed Sirett" wrote in message
newsan.2005.12.27.00.06.19.787075@makewrite. demon.co.uk...
On Mon, 26 Dec 2005 18:52:23 +0000, Nick wrote:

Hi Ed,

I was wondering if you had seen any / many
Wickes Combis, the 102,000 btu item ?
It is a Halstead, possibly the Ace High,
with a Wickes badge ?

The sheds and catalogues (Screwfux
and TollStation etc.) tend to rebadge
low end boilers to be sold on price.

I really must write the how to choose a boiler FAQ.

Please don't has you clearly don't know too much about them. 10 litre/min
from wall hung combis? Please. The FAQ needs to have correct and factual
information, nothing that is misleading, no old wives tales or personal
prejudices.


So you won't be contributing then?

I'm about half way through. I'll willingly take into consideration
everyones comments. I'm quite pleased with the generosity of the good
doctor's offer to edit it. ISTR that when he looked at the Sealed CH FAQ
he only got to the first paragraph before giving up and declaring the
work as 'incomplete' and 'wrong'.

What did you expect ?

I'm confident that the doctor will not interfere as interfere will require
effort thought and subjecting his work to criticism.

Well the first draft is up. See below.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

On Wed, 28 Dec 2005 22:04:59 +0000, Ed Sirett
wrote:



Well the first draft is up. See below.

I think that this covers the ground quite well, Ed, and I think that
it is useful to avoid putting specific makes and models in because
these change quite rapidly.

Would it be worth saying something about the different technology
types? e.g. basic, system, combi with/without storage, etc.
Changing type of system is a frequent question and involves a boiler
choice, or rather boiler choice may have unforeseen implications for
the unwary.





--

..andy

Ed Sirett wrote:
On Tue, 27 Dec 2005 23:38:11 +0000, raden wrote:

Well the first draft is up. See below.

Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

qany repair of less than £100 is worth doing. For boilers less than 20
years old allow another £50-£100 for each year less than 20./q

At first I thought this meant if boiler is say 15 yr old then 15*£100
but then it might make more sense if you meant (20-15)*£100? I don't
diagree with the principle but it might be expressed better: eg budget
£50-100 pa for repairs or replacement, the older it is the more you have
'saved' for its replacement?





--
David Clark

$message_body_include ="PLES RING IF AN RNSR IS REQIRD"

On Wed, 28 Dec 2005 23:00:42 +0000, Andy Hall wrote:

On Wed, 28 Dec 2005 22:04:59 +0000, Ed Sirett
wrote:



Well the first draft is up. See below.

I think that this covers the ground quite well, Ed, and I think that
it is useful to avoid putting specific makes and models in because
these change quite rapidly.

I also might get sued. wry smile


Would it be worth saying something about the different technology
types? e.g. basic, system, combi with/without storage, etc.
Changing type of system is a frequent question and involves a boiler
choice, or rather boiler choice may have unforeseen implications for
the unwary.

See the other thread "New FAQ" There's an effin mine field also.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

In article .com,
alanjones wrote:
Dan ignore all conflicting advice and go for a combi. It never ceases
to amaze me that English people love to store hot water in poorly
lagged hot water tanks. This is unheard of on the continent.

Does this mean they use properly lagged tanks on the continent? If so you
should be advised they are available here too. And have been for many
years...

--
*Never miss a good chance to shut up.*

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

alanjones wrote:

Dan ignore all conflicting advice and go for a combi. It never ceases
to amaze me that English people love to store hot water in poorly
lagged hot water tanks. This is unheard of on the continent. Combi's
are easier to install, there is no hot water storage tank and no header
tank in the loft.

What happens when the mains supply fails ? (Which happened to my
village on Christmas Eve)

Cheers,

John

"Ed Sirett" wrote in message
news
On Tue, 27 Dec 2005 23:38:11 +0000, raden wrote:

In message .uk, Ed
Sirett writes
On Tue, 27 Dec 2005 10:23:39 +0000, Andy Hall wrote:

On Tue, 27 Dec 2005 10:16:36 -0000, "Doctor Drivel"
wrote:


"Ed Sirett" wrote in message
newsan.2005.12.27.00.06.19.787075@makewrite .demon.co.uk...
On Mon, 26 Dec 2005 18:52:23 +0000, Nick wrote:

Hi Ed,

I was wondering if you had seen any / many
Wickes Combis, the 102,000 btu item ?
It is a Halstead, possibly the Ace High,
with a Wickes badge ?

The sheds and catalogues (Screwfux
and TollStation etc.) tend to rebadge
low end boilers to be sold on price.

I really must write the how to choose a boiler FAQ.

Please don't has you clearly don't know too much about them. 10
litre/min
from wall hung combis? Please. The FAQ needs to have correct and
factual
information, nothing that is misleading, no old wives tales or personal
prejudices.


So you won't be contributing then?

I'm about half way through. I'll willingly take into consideration
everyones comments. I'm quite pleased with the generosity of the good
doctor's offer to edit it. ISTR that when he looked at the Sealed CH FAQ
he only got to the first paragraph before giving up and declaring the
work as 'incomplete' and 'wrong'.

What did you expect ?

I'm confident that the doctor will not interfere as interfere will require
effort thought and subjecting his work to criticism.

From the man who can't tell the difference between a Part L and a fast
recovery cylinder.

wrote in message
oups.com...
alanjones wrote:

Dan ignore all conflicting advice and go for a combi. It never ceases
to amaze me that English people love to store hot water in poorly
lagged hot water tanks. This is unheard of on the continent. Combi's
are easier to install, there is no hot water storage tank and no header
tank in the loft.

What happens when the mains supply fails ? (Which happened to my
village on Christmas Eve)

Gas mains? If you want full backup, have one gas boiler and one run of LPG
bottles, and reserve genny to keep essential services going. I have not has
a water or gas cut ever. Electricity has been no more than 1 hour once in
blue moon. If you are rural with dicky supplies then take full and proper
precautions.

"Fentoozler" nospam@mapson wrote in message
...

I saw a great set-up the other day...

Unvented cylinder, heated via solar panels (actually evacuated tubes),
which then passed through a Worcester condensing boiler for DHW.

Do you mean a combi?

The boiler simply topped up any heat demand required. The cylinder sat at
25c even in the winter, therefore using a lot less energy to satisfy
demand. Also had an immersion in case of boiler problems.

Probably not that rare - first one I've seen though.

Not so rare. Look at the Eco-Homtec site as they have a boiler dedicated for
the task. It really improves combi performance having the inlet raised to
25C and above. I prefer a thermal store to have the solar heat dumped into,
and a heating or system boiler heat the store. Low pressure and faster DHW
rates, if you need high rates of course, not everyone does.

"Doctor Drivel" wrote in message
eenews.net...

"Fentoozler" nospam@mapson wrote in message
...

I saw a great set-up the other day...

Unvented cylinder, heated via solar panels (actually evacuated tubes),
which then passed through a Worcester condensing boiler for DHW.

Do you mean a combi?

The boiler simply topped up any heat demand required. The cylinder sat
at 25c even in the winter, therefore using a lot less energy to satisfy
demand. Also had an immersion in case of boiler problems.

Probably not that rare - first one I've seen though.

Not so rare. Look at the Eco-Homtec site as they have a boiler dedicated
for the task. It really improves combi performance having the inlet
raised to 25C and above. I prefer a thermal store to have the solar heat
dumped into, and a heating or system boiler heat the store. Low pressure
and faster DHW rates, if you need high rates of course, not everyone does.


It was a combi - a great system and not overly complicated to fit either.

I have the system you say you prefer above, evacuated tubes dumping heat via
a twin-coil cylinder (sealed for solar, open for boiler), the other coil
heated from my trusty old Glowworm BBU! Gets too hot in the summer though
(80c +), thinking about adding a rad and a zone valve to dump the heat when
necessary, shame to waste it though.

Angus

"Fentoozler" nospam@mapson wrote in message
news
"Doctor Drivel" wrote in message
eenews.net...

"Fentoozler" nospam@mapson wrote in message
...

I saw a great set-up the other day...

Unvented cylinder, heated via solar panels (actually evacuated tubes),
which then passed through a Worcester condensing boiler for DHW.

Do you mean a combi?

The boiler simply topped up any heat demand required. The cylinder sat
at 25c even in the winter, therefore using a lot less energy to satisfy
demand. Also had an immersion in case of boiler problems.

Probably not that rare - first one I've seen though.

Not so rare. Look at the Eco-Homtec site as they have a boiler dedicated
for the task. It really improves combi performance having the inlet
raised to 25C and above. I prefer a thermal store to have the solar heat
dumped into, and a heating or system boiler heat the store. Low pressure
and faster DHW rates, if you need high rates of course, not everyone
does.

It was a combi - a great system and not overly complicated to fit either.

It has an unvented cylinder, which required an annual service, and full of
pressurised water.

I have the system you say you prefer above, evacuated tubes dumping heat
via a twin-coil cylinder (sealed for solar, open for boiler), the other
coil heated from my trusty old Glowworm BBU!

BBU? Yuk.

Gets too hot in the summer though (80c +), thinking about adding a rad and
a zone valve to dump the heat when necessary, shame to waste it though.

Excessive heat could be problematical on an unvented cylinder. What you
could do is increase the thermal store size by adding another cylinder
instead of rads. Have the return from the main cylinder run through the
additional cylinders coil and either have a shunt pump to pump from one to
the other, or use gravity. Do you have a conventional cylinder or thermal
store which instantly heats cold mains water? A thermal store can easily
store water at 95C.

On Thu, 29 Dec 2005 18:23:24 -0000 Doctor Drivel wrote :
Not so rare. Look at the Eco-Homtec site as they have a boiler
dedicated for the task. It really improves combi performance
having the inlet raised to 25C and above.

You could do much the same at less cost by having a do-nothing store
in the combi feed. The water would gradually come up to the house
ambient (of course this heat is being provided by the combi) so go in
to the combi at 15-20 instead of the winter 5 or whatever.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm
[Latest version QSEDBUK 1.12 released 8 Dec 2005]

"Tony Bryer" wrote in message
...
On Thu, 29 Dec 2005 18:23:24 -0000 Doctor Drivel wrote :
Not so rare. Look at the Eco-Homtec site as they have a boiler
dedicated for the task. It really improves combi performance
having the inlet raised to 25C and above.

You could do much the same at less cost by having a do-nothing store
in the combi feed. The water would gradually come up to the house
ambient (of course this heat is being provided by the combi) so go in
to the combi at 15-20 instead of the winter 5 or whatever.

It would have to be tall thin cylinders with no insulation, and depends on
frequency if use. They take a time to get to ambient if cooled quickly to
5C will quite a time rise.

You could use the heat stored in radiators and use then radiators as a store
of heat. they would cool rapidly and when switched to CH re-heat rapidly
too. They will give 20-25C in summer and maybe even cool the house.

The heat in a full heating system can be used to pre-heat cold mains
pressure hot water. This can be done. I have seen this done using a plate
heat exchanger, pump, flowswitch and two check valves. The system should
not have thermostatic rad valves, or few of them. On a combi system:

- a by-pass pipe between the flow and return at the boiler
- on this pipe a re-heat plate heat exchanger is fitted
- The pump is fitted between the plate and the return by-pass pipe tee to
the return.
- A check valve between the pump and the plate
- A check valve on the boiler flow before the tee to the by-pass pipe.
- A flow switch on the cold mains water before the pre-heated plate heat
exchanger.

The check valve on the flow pipe ensure no flow back into the boiler,
although the internal 3-way valve should do this.
The check valve on the by-pass pipe ensure no short circuit in normal CH
operation.
The cold mains water runs through the pre-heat plate heat exchanger. This
pre-heated main water then runs into the combi as normal. When calling for
DHW the combi diverts to DHW only to heat the incoming cold water.
The flow of mains water is detected by the flow switch and switches on the
by-pass pump. This pumps water from the rads into the pre-heat plate heat
exchanger. This will raise the mains water substantially and the combi tops
up.

You can fill a bath up in a few minutes doing it this way. The rads cool
down a lot. This doesn't matter as when the system switches over to CH, the
boiler re-heats the rads ASAP, with loss in room temp so small it is not
noticeable to the occupants.

The combi flow rate in summer, when the CH is off is better than an average
flowrate combi as the water in the rads will be around 20 -25C when the CH
is off. This stored 20C plus heat is used to pre-heat the cold mains water,
which is around 10-12C. Depending on the efficiency of the plate heat
exchanger and power of the boiler, the flow rate may be very good, even in
summer. Cooling the rads also helps to cool the house in summer too.

A simple and cheap way to vastly improve the output of a combi.