In another thread

It was established in another thread that I have a leaking heat
exchanger coil in my hot cylinder. The system is a semi-gravity system
more than 25 years old.

I will at sometime in the future need to replace the aging boiler and
with that in mind, if I replace the cylinder myself, I would like to
replace it with a good quality fast recovery model with double thickness
insulation, etc.

Most of the specification sheets I have read say that this type of
cylinder should only be used in a fully pumped system. Is this just to
get the best performance out of the cylinder, or is there some real
technical reason they wont work in a gravity hot water system? Will
installing one in a gravity system damage anything?

If I can't fit this type of cylinder now, then I may as well consider
changing the boiler and converting to fully pumped as well.

Thanks,
BraileTrail

--

On Mon, 04 Jan 2010 21:42:16 +0000, BraileTrail wrote:

Most of the specification sheets I have read say that this type of
cylinder should only be used in a fully pumped system. Is this just to
get the best performance out of the cylinder, or is there some real
technical reason they wont work in a gravity hot water system? Will
installing one in a gravity system damage anything?

No, but the coil will be designed to give a lot of heat exchanger area for
fast recovery at the expense of higher thermal resistance than a
coil deigned for gravity circulation, so you're likely to get even worse
re-heating than the original unless you do convert to pumped.

You could just keep the cylinder, blank off the coil connections, buy a
PHE and bits and and use it as a DIY heatbank (see wiki).



--
John Stumbles -- http://yaph.co.uk

Eagles may soar, but weasels don't get sucked into jet engines.

In article ,
BraileTrail writes:
In another thread

It was established in another thread that I have a leaking heat
exchanger coil in my hot cylinder. The system is a semi-gravity system
more than 25 years old.

I will at sometime in the future need to replace the aging boiler and
with that in mind, if I replace the cylinder myself, I would like to
replace it with a good quality fast recovery model with double thickness
insulation, etc.

Most of the specification sheets I have read say that this type of
cylinder should only be used in a fully pumped system. Is this just to
get the best performance out of the cylinder, or is there some real
technical reason they wont work in a gravity hot water system? Will
installing one in a gravity system damage anything?

My _guess_ is the flow resistance through the coil might be
too high. Instead of one 22mm or 28mm coil, they increase the
coil surface area by having something like 4 microbore coils.
I'm guessing these will have higher flow resistance. No damage,
but heat input might be significantly reduced due to low flow.
Given that a gravity cylinder is effectively 'on' for ages
during the winter, this may not matter in practice, unless you
try having many baths or showers in quick succession.
If you found this to be the case, and it really didn't work,
you could always add a pump to the circuit.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

"BraileTrail" wrote in message
...
In another thread

It was established in another thread that I have a leaking heat exchanger
coil in my hot cylinder. The system is a semi-gravity system more than 25
years old.

I will at sometime in the future need to replace the aging boiler and with
that in mind, if I replace the cylinder myself, I would like to replace it
with a good quality fast recovery model with double thickness insulation,
etc.

Most of the specification sheets I have read say that this type of
cylinder should only be used in a fully pumped system. Is this just to get
the best performance out of the cylinder, or is there some real technical
reason they wont work in a gravity hot water system? Will installing one
in a gravity system damage anything?

If I can't fit this type of cylinder now, then I may as well consider
changing the boiler and converting to fully pumped as well.

Thanks,
BraileTrail

AS you are to replace the boiler soon, replacing the cylinder and updating
controls, maybe false economy. Consider a high flow quality combi boiler.
Look at the Remeha Avantaplus 39C, get the outside weather compensator
senor. You will not look back. And lots of space liberated.

"YAPH" wrote in message
...
On Mon, 04 Jan 2010 21:42:16 +0000, BraileTrail wrote:

Most of the specification sheets I have read say that this type of
cylinder should only be used in a fully pumped system. Is this just to
get the best performance out of the cylinder, or is there some real
technical reason they wont work in a gravity hot water system? Will
installing one in a gravity system damage anything?

No, but the coil will be designed to give a lot of heat exchanger area for
fast recovery at the expense of higher thermal resistance than a
coil deigned for gravity circulation, so you're likely to get even worse
re-heating than the original unless you do convert to pumped.

And if you are not satisfied with the performance could you not convert your
present system to being fully pumped?

--
Michael Chare

"Doctor Drivel" wrote in message
...

"BraileTrail" wrote in message
...
In another thread

It was established in another thread that I have a leaking heat exchanger
coil in my hot cylinder. The system is a semi-gravity system more than 25
years old.

I will at sometime in the future need to replace the aging boiler and
with that in mind, if I replace the cylinder myself, I would like to
replace it with a good quality fast recovery model with double thickness
insulation, etc.

Most of the specification sheets I have read say that this type of
cylinder should only be used in a fully pumped system. Is this just to
get the best performance out of the cylinder, or is there some real
technical reason they wont work in a gravity hot water system? Will
installing one in a gravity system damage anything?

If I can't fit this type of cylinder now, then I may as well consider
changing the boiler and converting to fully pumped as well.

Thanks,
BraileTrail

AS you are to replace the boiler soon, replacing the cylinder and updating
controls, maybe false economy. Consider a high flow quality combi boiler.
Look at the Remeha Avantaplus 39C, get the outside weather compensator
senor. You will not look back. And lots of space liberated.

And you can join the ranks of those like my brother who spent three weeks
with no heating or hot water earier in December thank to the lack of
cylinder & immersion heater.

Tim

Tim Downie wrote:

And you can join the ranks of those like my brother who spent three
weeks with no heating or hot water earier in December thank to the lack
of cylinder & immersion heater.


This has just happened to a guy at work. Currently living in one room
with a fan heater and borrowing friend's showers.

Andy

"Tim Downie" wrote in message
...

"Doctor Drivel" wrote in message
...

"BraileTrail" wrote in message
...
In another thread

It was established in another thread that I have a leaking heat
exchanger coil in my hot cylinder. The system is a semi-gravity system
more than 25 years old.

I will at sometime in the future need to replace the aging boiler and
with that in mind, if I replace the cylinder myself, I would like to
replace it with a good quality fast recovery model with double thickness
insulation, etc.

Most of the specification sheets I have read say that this type of
cylinder should only be used in a fully pumped system. Is this just to
get the best performance out of the cylinder, or is there some real
technical reason they wont work in a gravity hot water system? Will
installing one in a gravity system damage anything?

If I can't fit this type of cylinder now, then I may as well consider
changing the boiler and converting to fully pumped as well.

Thanks,
BraileTrail

AS you are to replace the boiler soon, replacing the cylinder and
updating controls, maybe false economy. Consider a high flow quality
combi boiler. Look at the Remeha Avantaplus 39C, get the outside weather
compensator senor. You will not look back. And lots of space liberated.

And you can join the ranks of those like my brother who spent three weeks
with no heating or hot water earier in December thank to the lack of
cylinder & immersion heater.

A cylinder does not provide DHW. You can have a small back-up instant
electric water heater to give DHW to a tap and shower - cost is around £100.
Fine until the combi is back up and running.

If you want full electric CH and DHW backup you go thermal store/heat bank.

Or maybe fit a £300 B&Q cheapo combi as back only, which I have done a few
times. Use the same gas pipe and a throw over electric switch so both
combis cannot be on at the same time. Very cost effective and still saves
space.

"Andy Champ" wrote in message
. uk...
Tim Downie wrote:

And you can join the ranks of those like my brother who spent three weeks
with no heating or hot water earier in December thank to the lack of
cylinder & immersion heater.

This has just happened to a guy at work. Currently living in one room
with a fan heater and borrowing friend's showers.

He could have a small back-up instant electric water heater, the outlet of
the combi runs through it when it is off. Fine until the combi is back up
and running. He has heat via the fan heater, which is probably fine untill
the combi is back up.

In an earlier contribution to this discussion,
Doctor Drivel wrote:


A cylinder does not provide DHW.

It does on the planet I live on! And if it has an immersion heater for
emergency use, it *continues* to provide DHW even if the boiler isn't
working.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

"Roger Mills" wrote in message
...
In an earlier contribution to this discussion,
Doctor Drivel wrote:


A cylinder does not provide DHW.

It does

Typo should have been CH. Now read again.

In an earlier contribution to this discussion,
Doctor Drivel wrote:

"Roger Mills" wrote in message
...
In an earlier contribution to this discussion,
Doctor Drivel wrote:


A cylinder does not provide DHW.

It does

Typo should have been CH. Now read again.

No-one was suggesting that a cylinder provided CH - but simply that with a
stored HW system you don't have all your eggs in one basket, and you can
still have hot water even if there's no CH. The same is *not* true if you
have a combi.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

"Roger Mills" wrote in message
...
In an earlier contribution to this discussion,
Doctor Drivel wrote:

"Roger Mills" wrote in message
...
In an earlier contribution to this discussion,
Doctor Drivel wrote:


A cylinder does not provide DHW.

It does

Typo should have been CH. Now read again.

No-one was suggesting that a cylinder provided CH - but simply that with a
stored HW system you don't have all your eggs in one basket, and you can
still have hot water even if there's no CH.

I know that.

The same is *not* true if you have a combi.

What you are on about is backup if the boiler is down. That can be had
cheaply with a combi by installing a small in-line instant water heater that
takes little space. I clearly explained this.

In installation costs it will be cheaper having a combi and an in-line
electric water heater, than a boiler/cylinder/zone valves/controls/immersion
heater/tank in the loft. For heating backup a small, cheap fan heater may be
OK for a day or so. Second hand you can pick them up used for a few pounds.

If you are obsessed with having a cylinder ina normal house for some
perverse reason, then go for a thermal store/heat bank which gives 100% CH &
DHW backup and high pressure DHW.

On Wed, 06 Jan 2010 21:54:56 +0000, Doctor Drivel wrote:

A cylinder does not provide DHW.

Does if it has an electric immersion heater.

You can have a small back-up instant
electric water heater to give DHW to a tap and shower - cost is around
£100.

Plus the (not insignificant cost) of providing a 40A or more supply to the
beast.


--
John Stumbles -- http://yaph.co.uk

Xenophobia? Sounds a bit foreign to me.

Andy Champ wrote:

This has just happened to a guy at work. Currently living in one room
with a fan heater and borrowing friend's showers.

Probably slightly more civilised than the outdoor shower I rigged up
here while rebuilding the bathroom. The old mouldy shower tray, and a
wrap-around of blue poly-tarp suspended from the wall of the house.

Meant to be for a week, ended up being for a month...

Mind you, the actual shower itself was better than before, due to the
extra head of being downstairs :-)

Pete

"Doctor Drivel" wrote in message
...

"Roger Mills" wrote in message
...
In an earlier contribution to this discussion,
Doctor Drivel wrote:

"Roger Mills" wrote in message
...
In an earlier contribution to this discussion,
Doctor Drivel wrote:


A cylinder does not provide DHW.

It does

Typo should have been CH. Now read again.

No-one was suggesting that a cylinder provided CH - but simply that with
a stored HW system you don't have all your eggs in one basket, and you
can still have hot water even if there's no CH.

I know that.

The same is *not* true if you have a combi.

What you are on about is backup if the boiler is down. That can be had
cheaply with a combi by installing a small in-line instant water heater
that takes little space. I clearly explained this.

Yeah but, how many plumbers advise their clients about the lack of back up
or install any sort of back up system whilst they're ripping out an old
cylinder system? Damn few I'll bet. I've never met a combi owner with any
sort of back up.

Tim

"Tim Downie" wrote in message
...

"Doctor Drivel" wrote in message
...

"Roger Mills" wrote in message
...
In an earlier contribution to this discussion,
Doctor Drivel wrote:

"Roger Mills" wrote in message
...
In an earlier contribution to this discussion,
Doctor Drivel wrote:


A cylinder does not provide DHW.

It does

Typo should have been CH. Now read again.

No-one was suggesting that a cylinder provided CH - but simply that with
a stored HW system you don't have all your eggs in one basket, and you
can still have hot water even if there's no CH.

I know that.

The same is *not* true if you have a combi.

What you are on about is backup if the boiler is down. That can be had
cheaply with a combi by installing a small in-line instant water heater
that takes little space. I clearly explained this.

Yeah but, how many plumbers advise their clients about the lack of back up
or install any sort of back up system whilst they're ripping out an old
cylinder system?

Plumbers are good for drains.

Damn few I'll bet. I've never met a combi owner with any sort of back up.

It is easy to do. I just run the bathroom basin and shower through the
in-line heater. A kitchen always has a kettle and with dishwashers and
washing machines the kitchen is covered.

As I said I have done few with a super cheap combi as backup. Not the sort
as the main combi which will be a quality model, but OK to use once every 7
years for a few days, to give whole house backup, with reduced DHW as it
will be a low kW model. Just throw a switch and it works. Just an extra
£300 or so. the cheapest you can get. Price up a quality combi and a B&Q
cheapo using the same gas supply pipe to cut installation costs, to a
cylinder/boiler/tank/etc, and it still comes out cheaper and still little
space used. Little extra pipe is used if fitted next to the main combi.

Why some combi makers do not have a small electric backup heater inside is
beyond me. It must be a good selling point. Gledhill's thermal stores had
one if the boiler went down, that automatically came in.

"YAPH" wrote in message
...
On Wed, 06 Jan 2010 21:54:56 +0000, Doctor Drivel wrote:

A cylinder does not provide DHW.

Does if it has an electric immersion heater.

You can have a small back-up instant
electric water heater to give DHW to a tap and shower - cost is around
£100.

Plus the (not insignificant cost) of providing a 40A or more supply to the
beast.

The same cost wiring up an immersion. The heater will be 7 to 9kW so not
that great of an expense. I have used existing immersion cables as the
cylinder was ripped out leaving a large space to put a very small box on the
wall. The cables were man enough.

You could fit a small 15 litre 2kW storage water heater using an existing
2.5mm cable. Heated to 60C, or more, it will give a ~5 minutes shower at 5
litres/min. OK for backup. Gets you wet and with hot water.

Fitting in a small instant in-line water heater locally at the kitchen tap
permanently switched on, not for backup, can eliminate the cold dead leg
delay. Once the cheaper to heat water, heated by gas, comes in from a combi
or cylinder the electric heater switches out. This can be cheaper than
running a secondary circulation pump for only a remote tap(s), such as a
kitchen. If on a water meter it cuts down the water bills as well, so maybe
well worth it.

On Thu, 07 Jan 2010 09:17:58 +0000, Doctor Drivel wrote:

Plumbers are good for drains.

I'm not - I don't have pressure jetting equipment and CCTV cameras etc. -
and I don't suppose many other plumbers do either, any more than a pure
plumber has the expertise and tools to do heating.

....

Why some combi makers do not have a small electric backup heater inside
is beyond me. It must be a good selling point. Gledhill's thermal
stores had one if the boiler went down, that automatically came in.

sigh! because a small electric backup heater in a combi would be about
as much use as a chocolate teapot. For instantaneous water heating you
need a large - as large as you can manage - electric heater: 8.5 kW
minimum - and that's not going to run off the boiler's 3A fused spur, is
it? It's not even going to run off the local ring main, as Gledhill's 3kW
immersion heater and the immersions in a bazillion and one gravity hot
water systems can do. If the boiler installation is next door to the CU
then it's not too much of a problem, but if (to take a wildly improbable
and contrived scenario :-|) the CU is in the cupboard under the stairs and
the boiler is at the back of a back addition in a terraced house, then
you're looking at running maybe 10 or 15m of at least 6mm^2 - possibly
10mm^2 - cable to it. Do-able, but not trivial, and not a trivial extra
cost for the day or two per year when, probably, on average, you're likely
to need it.



--
John Stumbles -- http://yaph.co.uk

Question Authority

On Thu, 07 Jan 2010 09:34:11 +0000, Doctor Drivel wrote:

"YAPH" wrote in message
...
On Wed, 06 Jan 2010 21:54:56 +0000, Doctor Drivel wrote:

A cylinder does not provide DHW.

Does if it has an electric immersion heater.

You can have a small back-up instant
electric water heater to give DHW to a tap and shower - cost is around
£100.

Plus the (not insignificant cost) of providing a 40A or more supply to the
beast.

The same cost wiring up an immersion. The heater will be 7 to 9kW so not
that great of an expense. I have used existing immersion cables as the
cylinder was ripped out leaving a large space to put a very small box on the
wall. The cables were man enough.

Well, yes: one sees electric showers (same current demand as what we're
talking about) hooked up on 2.5 or 4mm^2 cable, but for a competent,
professional installation rather than DIY (in the pejorative sense of the
word) one needs to run properly-specified adequately-sized cable.

--
John Stumbles -- http://yaph.co.uk

If we'd known how much fun grandchildren are
we'd have had them first

"YAPH" wrote in message
...
On Thu, 07 Jan 2010 09:17:58 +0000, Doctor Drivel wrote:

Plumbers are good for drains.

I'm not - I don't have pressure jetting equipment and CCTV cameras etc. -
and I don't suppose many other plumbers do either, any more than a pure
plumber has the expertise and tools to do heating.

...

Why some combi makers do not have a small electric backup heater inside
is beyond me. It must be a good selling point. Gledhill's thermal
stores had one if the boiler went down, that automatically came in.

sigh! because a small electric backup heater in a combi would be about
as much use as a chocolate teapot. For instantaneous water heating you
need a large - as large as you can manage - electric heater: 8.5 kW
minimum - and that's not going to run off the boiler's 3A fused spur, is
it? It's not even going to run off the local ring main, as Gledhill's 3kW
immersion heater and the immersions in a bazillion and one gravity hot
water systems can do. If the boiler installation is next door to the CU
then it's not too much of a problem, but if (to take a wildly improbable
and contrived scenario :-|) the CU is in the cupboard under the stairs and
the boiler is at the back of a back addition in a terraced house, then
you're looking at running maybe 10 or 15m of at least 6mm^2 - possibly
10mm^2 - cable to it. Do-able, but not trivial, and not a trivial extra
cost for the day or two per year when, probably, on average, you're likely
to need it.



--
John Stumbles -- http://yaph.co.uk



Prolly best to fit two combis then:-) Just in case.

Adam

Thanks to everyone for the comments and suggestions.

A large combi *sounds* like a good idea, but my own experience with them
warns me away from them.

Thanks,
BraileTrail

--

"YAPH" wrote in message
...

sigh! because a small electric backup heater in
a combi would be about as much use as a chocolate
teapot.

sigh

A small instant DHW electric heater can be installed as a "backup", give 5
litres/min. It can have a heavier cable if required. People will go for
it. Pay attention.

On Thu, 07 Jan 2010 14:41:16 +0000, ARWadsworth wrote:

Prolly best to fit two combis then:-) Just in case.

G'wan, make it 3 just to be on the safe side. Sod's law says the backup
will be bust when you need it.

--
John Stumbles

I'm more non-competitive than you

"YAPH" wrote in message
...

but for a competent,
professional installation rather than DIY (in the pejorative sense of the
word) one needs to run properly-specified adequately-sized cable.

I would assume you would have to.

"BraileTrail" wrote in message
...
Thanks to everyone for the comments and suggestions.

A large combi *sounds* like a good idea, but my own experience with them
warns me away from them.

That is like say I bought a cheap crap car and it was bad so all cars are
bad. Buy quality.

"John Stumbles" wrote in message
...
On Thu, 07 Jan 2010 14:41:16 +0000, ARWadsworth wrote:

Prolly best to fit two combis then:-) Just in case.

G'wan, make it 3 just to be on the safe side. Sod's law says the backup
will be bust when you need it.

You can go on and on. Do some calculation on pounds and a second small
cheapo backup combi is very cheap to do. It gives FULL backup. Never
thought of it did you?

"ARWadsworth" wrote in message
...

Prolly best to fit two combis then:-) Just in case.

This one is learning.

"Doctor Drivel" wrote in message
...

"ARWadsworth" wrote in message
...

Prolly best to fit two combis then:-) Just in case.

This one is learning.

Nice one:-)

The Saunier Duval engineer whose house I did some work in did indeed have
two boilers in the loft. One was for backup.

The back up was a Baxi.

Adam

"ARWadsworth" wrote in message
m...

"Doctor Drivel" wrote in message
...

"ARWadsworth" wrote in message
...

Prolly best to fit two combis then:-) Just in case.

This one is learning.

Nice one:-)

The Saunier Duval engineer whose house I did some work in did indeed have
two boilers in the loft. One was for backup.

The back up was a Baxi.

Do you have point?