I am planning a new central heating for my house which is a 3-bed semi.
There is currently only myself living here, but I may want to rent the
place out to a family at some stage. I need to decide between a combi
(sealed) system vs a conventional system with expansion tank.

Sited in my loft, is a Fortic cylinder with integral expansion tank. It
appears to have an internal coil (not in use), as there are two unused pipe
connections on it. I'm currently using the Fortic cylinder as an immersion
heater to heat my tap water.

I gather I'd consume less gas if I choose a combi, rather than a
conventional boiler. However, my experience of combis is that they are
expensive to maintain. I always envied people with older systems that seem
to require virtually no maintenance. Even slight leaks can be ignored in a
not-sealed conventional system, I gather.

Has anyone got any views on the overall cost (money + trouble) of
installing and running a sealed combi system vs. a conventional system?

Thanks for any advice...

Al

On 06/09/2012 16:03, AL_n wrote:
I am planning a new central heating for my house which is a 3-bed semi.
There is currently only myself living here, but I may want to rent the
place out to a family at some stage. I need to decide between a combi
(sealed) system vs a conventional system with expansion tank.

Sited in my loft, is a Fortic cylinder with integral expansion tank. It
appears to have an internal coil (not in use), as there are two unused pipe
connections on it. I'm currently using the Fortic cylinder as an immersion
heater to heat my tap water.

I gather I'd consume less gas if I choose a combi, rather than a
conventional boiler. However, my experience of combis is that they are
expensive to maintain. I always envied people with older systems that seem
to require virtually no maintenance. Even slight leaks can be ignored in a
not-sealed conventional system, I gather.

Has anyone got any views on the overall cost (money + trouble) of
installing and running a sealed combi system vs. a conventional system?

Thanks for any advice...

Al


Modern or old house? Large or small? I use a small holiday place (modern
semi) where a combi works absolutely fine, but all the pipe runs are
very short: it was designed around the services. I have a rambling 18th
century house (originally two cottages) where the pipe runs are a
nightmare. I've had two inadequate combis over 20-odd years and have
just replaced the boiler with a conventional one with a hot tank in the
loft. Lots of lovely hot water thanks to a Stuart Turner pump!

With a combi, the issue is not so much leaks, but there is more to go
wrong with the secondary heat exchanger and the control system.

In article ,
"AL_n" writes:
I am planning a new central heating for my house which is a 3-bed semi.
There is currently only myself living here, but I may want to rent the
place out to a family at some stage. I need to decide between a combi
(sealed) system vs a conventional system with expansion tank.

Those are not either/or options - they are two unrelated things.

You can have a combi or a system boiler. The combi has extra guts
inside to do instant water heating, which the system boiler is
missing. If a system boiler is going to heat the hot water, it
needs a separate hot water storage tank/cylinder.

In theory, either of these could be sealed systems or vented with
a header tank in the loft. In practice, I suspect you may find that
just about all boilers only specify sealed operation today. It was
heading that way 10 years ago when I did my system, and no one was
installing new vented systems even back then - you only got a vented
system when retrofitting a new boiler into an existing one, and even
them, many plumbers would convert it to a sealed system at that point.

Sited in my loft, is a Fortic cylinder with integral expansion tank. It
appears to have an internal coil (not in use), as there are two unused pipe
connections on it. I'm currently using the Fortic cylinder as an immersion
heater to heat my tap water.

If you want to heat that with the boiler, you would use a system
boiler. You would probably also want a sealed system, as you would
struggle to get a vented tank high enough to drive the coil, yet
lower than the header tank on the Fortic.

How good is the fortic, in terms of wear/corrosion, and insulation?
Unless it's good on both counts, designing your system around
reusing it might not be a good idea.

I gather I'd consume less gas if I choose a combi, rather than a
conventional boiler.

Why? That depends on a number of things.
Could be true for a single person, but probably less likely with
a family and a well insulated tank.

However, my experience of combis is that they are
expensive to maintain. I always envied people with older systems that seem
to require virtually no maintenance. Even slight leaks can be ignored in a
not-sealed conventional system, I gather.

They shouldn't be - they can turn into dry rot, etc.

Has anyone got any views on the overall cost (money + trouble) of
installing and running a sealed combi system vs. a conventional system?

For a rented property, if you have the space, I would use system
boiler and hot water storage tank, with back-up electric immersion,
because this gives you some redundancy, which means a boiler failure
is not quite such an emergency, and a system boiler has less to go
wrong in it than a combi. (Another option would be an instant in-line
electric heater backup for a combi.)

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

newshound wrote in news:5048c0f4$0$56103$c3e8da3
:

Modern or old house? Large or small?

It's half ancient and half modern. Half of it is solid stone, and the other
half is cavity blockwork. Overall, it's not a big place, and the longest
pipe run would be about 10 mtrs.

With a combi, the issue is not so much leaks, but there is more to go
wrong with the secondary heat exchanger and the control system.

Yes; I had those sort of problems in my last house, where I installed my
own combi susytem. Come to think of it, leaks weren't too much of an issue.
Fter finding I had to replace the secondary heat exchanger about once every
two years, I installed a phosphate doser, hoping it would help, but I sold
the place shortly after that, so I never found out.

Thanks for the input,

Al

(Andrew Gabriel) wrote in
:

How good is the fortic, in terms of wear/corrosion, and insulation?
Unless it's good on both counts, designing your system around
reusing it might not be a good idea.

It does look pretty old and decrepit, although I've never had any problems
with it, using it as an immersion heater. I must say, I'm not all that keen
on having part of the system in the loft, because the older I get, the less
excited I get about crawling around up there to sort out some problem.

I gather I'd consume less gas if I choose a combi, rather than a
conventional boiler.

Why? That depends on a number of things.
Could be true for a single person, but probably less likely with
a family and a well insulated tank.

Thanks for pointing that out. It does make sense.

For a rented property, if you have the space, I would use system
boiler and hot water storage tank, with back-up electric immersion,
because this gives you some redundancy, which means a boiler failure
is not quite such an emergency, and a system boiler has less to go
wrong in it than a combi. (Another option would be an instant in-line
electric heater backup for a combi.)

Some helpful insights there; many thanks.. I guess I can keep the existing
immersion heater in service, as a backup tap-water heater, if I install a
combi, yes?

Al

"AL_n" wrote in
:


Some more questions:

1) Is it easier to regulate the temperature of the tap water, using a combi
system? (I'm particularly thinking of the shower, which needs to always be
at the same temperature.) If I were to use a system boiler, some of the DHW
pipework would be running through a draughty loft, unless I relocate the
Fortic tank somewhere on the landing.

2) If I install a combi, the heated water will reach the taps quicker, than
it would from the Fortic tank in my loft. Would this difference tend to be
noticeable, in terms of how long one has to wait for the water to run hot,
after turning on a tap?

3) My gas pressure is borderline, as I am at the end of a long run of gas
main. Is that likely to pose a problem with a combi as opposed to a system
boiler?

4) Someone once told me to always site the boiler in a warm, place like a
broom cuboard, because if it's in a cold room (e.g., a garage), it will
keep firing up all the time and wasting a lot of gas. Am I right in
thinking that this problem could be overcome by simply by connecting the
boiler to a thermstat that is in a warm part of the house?

Thanks,
A

AL_n wrote:
"AL_n" wrote in
:


Some more questions:

1) Is it easier to regulate the temperature of the tap water, using a combi
system? (I'm particularly thinking of the shower, which needs to always be
at the same temperature.) If I were to use a system boiler, some of the DHW
pipework would be running through a draughty loft, unless I relocate the
Fortic tank somewhere on the landing.

No. Combi systems unless they are Ginormous always run cold or show
pathetic throughputs of water flow.

You need some form of ho****er storage and a pump or mains pressure to
get a decent shower.

Coupling heat banks to combis is a bodge solution = once you have a hot
water storage system there is little point in a combi.

They are cheap low physical fopotprint solutions to domestic heating and
a patheic DHW supply.

2) If I install a combi, the heated water will reach the taps quicker, than
it would from the Fortic tank in my loft. Would this difference tend to be
noticeable, in terms of how long one has to wait for the water to run hot,
after turning on a tap?
No.
Unless you are inches away from the combi.


3) My gas pressure is borderline, as I am at the end of a long run of gas
main. Is that likely to pose a problem with a combi as opposed to a system
boiler?

Cant say. Might do.

4) Someone once told me to always site the boiler in a warm, place like a
broom cuboard, because if it's in a cold room (e.g., a garage), it will
keep firing up all the time and wasting a lot of gas. Am I right in
thinking that this problem could be overcome by simply by connecting the
boiler to a thermstat that is in a warm part of the house?


Its good to site boilers in the house but not for the ******** reasons
you have been given.

They generate a lot of heat that doesn't go into the water. Might as
well have it IN the house.

Also in the event that there is a hard frost and you aren't there, amd
leave the heating off, water pipes connected to outside boilers can freeze.

That's why outside boilers in sheds have frost stats to fire em up a
little in the cold


Thanks,
A


--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

In article ,
"AL_n" writes:
"AL_n" wrote in
:


Some more questions:

1) Is it easier to regulate the temperature of the tap water, using a combi
system? (I'm particularly thinking of the shower, which needs to always be
at the same temperature.)

No, it's easier with a storage tank, as the temperature remains
constant irrespective of draw-off rate. With a combi, it depends
on the quality of the combi, but a change in flow rate (e.g.
opening a tap somewhere else) is very likely to change the
temperature and/or the hot water flowrate into the shower.
Ideally, for a shower running from an instant water heater, you
want a fast-acting (bi-metalic) thermostatic shower valve to try
and maintain the temperature in the face of sudden changes in
hot water temperature and/or pressure/flow rate. For a storage
tank system, you can use a cheaper slower acting wax pellet
shower mixer, or even a manual non-thermostatic mixer, because
the water temperature and pressure is not going to change suddenly.
OTOH, you might need a shower pump if you don't have much head of
water.

If I were to use a system boiler, some of the DHW
pipework would be running through a draughty loft, unless I relocate the
Fortic tank somewhere on the landing.

It is a good idea to consider the location of the stored hot
water or the combi, with a view of minimising pipe runs,
particularly to sinks and wash basins where you only want hot
water for a moment, and it's a waste to have to run off loads
of cold before the hot comes through. Not important for a bath
or shower where you're going to run lots of water anyway.
Being in the loft means you also have to protect against frost.

2) If I install a combi, the heated water will reach the taps quicker, than
it would from the Fortic tank in my loft. Would this difference tend to be
noticeable, in terms of how long one has to wait for the water to run hot,
after turning on a tap?

Yes.

There is another option, you could use a combi and a stored
water system, each supplying outlets near them, but that's
probably the worst option unless you have a compelling use
case that fits it well, such as multiple simultaneous baths
and showers.

3) My gas pressure is borderline, as I am at the end of a long run of gas
main. Is that likely to pose a problem with a combi as opposed to a system
boiler?

Could be - combis tend to be higher power for the instant
water heating. Often a house needs significantly less for
the heating, and as the hot water cylinder heats over time,
you can normally ignore the extra load that might need.
Do you know what your max gas rate is, and what other gas
loads you currently have? A normal domestic meter can go
up to around 55kW. If there's a flow problem into your gas
governor, they may be able to turn up the street supply
pressure to compensate, if it's not already at max.
Otherwise, I don't know what their responsibility is for
fixing their supply/pipework network if you can't get
enough gas.

4) Someone once told me to always site the boiler in a warm, place like a
broom cuboard, because if it's in a cold room (e.g., a garage), it will
keep firing up all the time and wasting a lot of gas. Am I right in
thinking that this problem could be overcome by simply by connecting the
boiler to a thermstat that is in a warm part of the house?

He's probably thinking of built-in frost protection. How
that works will depend on the boiler. Some combis also keep
a little hot water ready to run instantly, which means they
have to keep it heated up. Sometimes you can turn this
preheating function off.

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

(Andrew Gabriel) wrote in news:k2ansg$vl1$3
@dont-email.me:

Do you know what your max gas rate is, and what other gas
loads you currently have?

All I can remember is that when Transco installed a new gas meter a few
months ago, he commented that my gas pressure was "only just within the
permissible range" or words to that effect. I can't remember the figure he
mentioned.

Apart from a potential boiler, I have a gas cooker and one medium-sized
radiant gas fire.

Thanks to everyone for the very helpful input.

A

On 06/09/2012 19:16, AL_n wrote:
(Andrew Gabriel) wrote in news:k2ansg$vl1$3
@dont-email.me:

Do you know what your max gas rate is, and what other gas
loads you currently have?

All I can remember is that when Transco installed a new gas meter a few
months ago, he commented that my gas pressure was "only just within the
permissible range" or words to that effect. I can't remember the figure he
mentioned.

Don't quite understand that. The main should be at a significantly
higher pressure than the house has, and the regulator in the meter
should give you the right pressure in the house. Unless you are on very
old supply, and/or a long way from any other customers.

On 06/09/2012 18:30, Owain wrote:
On Sep 6, 4:41 pm, (Andrew Gabriel) wrote:
For a rented property, if you have the space, I would use system
boiler and hot water storage tank, with back-up electric immersion,
because this gives you some redundancy, which means a boiler failure
is not quite such an emergency,

Absolutely.

Loss of space heating is inconvenient, but fan heaters will do for a
few days if need arises. Tenants won't put up with loss of hot water.

Another option is a combi for a shower, and HW cyl for the bath etc.

With a condensing boiler watch how you run the condensate pipe as
that's a common cause of lockout errors if it freezes.

Owain


+1 (on each point)

On 06/09/2012 16:03, AL_n wrote:

I am planning a new central heating for my house which is a 3-bed semi.
There is currently only myself living here, but I may want to rent the
place out to a family at some stage. I need to decide between a combi
(sealed) system vs a conventional system with expansion tank.

That's not a one Vs the other argument. Boilers can be sealed system or
vented. Hot water can be from a combi or a hot water cylinder (which can
also be sealed or vented) - you can have them in any combination as
well. E.g. combi with vented heating system or heating only boiler with
a sealed primary circuit etc.

Sited in my loft, is a Fortic cylinder with integral expansion tank. It
appears to have an internal coil (not in use), as there are two unused pipe
connections on it. I'm currently using the Fortic cylinder as an immersion
heater to heat my tap water.

I gather I'd consume less gas if I choose a combi, rather than a
conventional boiler. However, my experience of combis is that they are
expensive to maintain. I always envied people with older systems that seem
to require virtually no maintenance. Even slight leaks can be ignored in a
not-sealed conventional system, I gather.

Depends on if you prefer dry rot to boiler problems...

Has anyone got any views on the overall cost (money + trouble) of
installing and running a sealed combi system vs. a conventional system?

Yes plenty...

Have a read of some of the background first so we can all talk the same
language:

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

also look at Ed's boiler choice FAQ:

http://www.makewrite.demon.co.uk/BoilerChoice.html



--
Cheers,

John.

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

On 06/09/2012 19:16, AL_n wrote:
(Andrew Gabriel) wrote in news:k2ansg$vl1$3
@dont-email.me:

Do you know what your max gas rate is, and what other gas
loads you currently have?

All I can remember is that when Transco installed a new gas meter a few
months ago, he commented that my gas pressure was "only just within the
permissible range" or words to that effect. I can't remember the figure he
mentioned.

The static pressure coming out of your gas governor will normally be in
the upper 20's millibars. When actually flowing it should regulate it to
21 mbar at the meter. That then leaves you 1 mbar to play with as losses
in the internal pipework to deliver gas at the 20 mbar most appliances
are nominally designed for.

Having said that, many do have wider operating limits then the
theoretical limits.

Apart from a potential boiler, I have a gas cooker and one medium-sized
radiant gas fire.

Thanks to everyone for the very helpful input.

A



--
Cheers,

John.

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

On 06/09/2012 18:30, Owain wrote:
On Sep 6, 4:41 pm, (Andrew Gabriel) wrote:
For a rented property, if you have the space, I would use system
boiler and hot water storage tank, with back-up electric immersion,
because this gives you some redundancy, which means a boiler failure
is not quite such an emergency,

Absolutely.

Loss of space heating is inconvenient, but fan heaters will do for a
few days if need arises. Tenants won't put up with loss of hot water.

Another option is a combi for a shower, and HW cyl for the bath etc.

An often overlook option it seems - many seem to forget that a combi can
still be wired up with zone valves etc just like a normal boiler and
heat a cylinder etc.

With a condensing boiler watch how you run the condensate pipe as
that's a common cause of lockout errors if it freezes.

The British gas "installed in the loft" setups seeming particularly
prone to that one.


--
Cheers,

John.

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

On 06/09/2012 18:50, The Natural Philosopher wrote:
AL_n wrote:
"AL_n" wrote in
:

Some more questions:

1) Is it easier to regulate the temperature of the tap water, using a
combi system? (I'm particularly thinking of the shower, which needs to
always be at the same temperature.) If I were to use a system boiler,
some of the DHW pipework would be running through a draughty loft,
unless I relocate the Fortic tank somewhere on the landing.

No. Combi systems unless they are Ginormous always run cold or show
pathetic throughputs of water flow.

You need some form of ho****er storage and a pump or mains pressure to
get a decent shower.

Can't see why you think that... Many modern showers are designed to run
on around 7 to 10 lpm - well within the reaches of even the most feeble
combi.

If you want giant soaker heads and multiple body jets, then sure, go for
stored hot water.

In the previous house the 35kW combi managed two reasonable showers at
once (i.e. both about twice to three times as good as an electric
shower), or one very good one with a bit of capacity to spare.

I am not suggesting that a combi is a panacea for all ills, but one
ought not let your dogma cloud the issue. Showers are playing to their
strengths.

Coupling heat banks to combis is a bodge solution = once you have a hot
water storage system there is little point in a combi.

I can think of applications where a combi and stored hot water would
work quite well... in fact its a solution I considered for this house.
(Cylinder in the middle of the house with all the bathrooms clustered in
close proximity, and boiler at the far corner of the house adjacent to
the util and kitchen. DHW from the combi would be an effective way of
getting potable hot water in the kitchen without the long dead leg to
run off from the cylinder, or the need for secondary circulation loops).

They are cheap low physical fopotprint solutions to domestic heating and
a patheic DHW supply.

Quick and easy to install so popular with builders etc. The boilers
themselves are no cheaper than system boiler though (not surprising
since most system boilers and combis are built on the same platform)

4) Someone once told me to always site the boiler in a warm, place
like a broom cuboard, because if it's in a cold room (e.g., a garage),
it will keep firing up all the time and wasting a lot of gas. Am I
right in thinking that this problem could be overcome by simply by
connecting the boiler to a thermstat that is in a warm part of the house?


Its good to site boilers in the house but not for the ******** reasons
you have been given.

I would have said it is actually a valid reason. Modern boilers have
frost protection built in, and so in cold environments will cycle to
keep themselves warm even if there is no external demand. However the
amount of cycling required is only minimal - a brief fire every few
hours probably.

They generate a lot of heat that doesn't go into the water. Might as
well have it IN the house.

Modern HE boilers generate very little heat from the boiler case itself.

In the past it was common to not fit a rad in the room with the boiler
since its waste heat would keep the room warm. With a boiler capable of
achieving over 95% efficiency, there is not going to be a couple of kW
slopping out from the casework.

--
Cheers,

John.

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

In article ,
John Rumm writes:
On 06/09/2012 18:50, The Natural Philosopher wrote:
They generate a lot of heat that doesn't go into the water. Might as
well have it IN the house.

Modern HE boilers generate very little heat from the boiler case itself.

Yes, the design of my Keston is that the heat that does leak
out the sides of the heat exchanger is picked up by the air
intake, and carried back into the heat exchanger as pre-warmed
air for the burner.

In the past it was common to not fit a rad in the room with the boiler
since its waste heat would keep the room warm. With a boiler capable of
achieving over 95% efficiency, there is not going to be a couple of kW
slopping out from the casework.

When designing my system, I looked for the figure for heat
loss from boiler casing and couldn't find it, so I assumed
200W. This turns out to be wrong, due to the above. If it's
been on a very long time, there's a warm patch in the middle
of the front just near the heat exchanger, but it probably
amounts to only a few tens of watts max.

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

John Rumm wrote in
o.uk:


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

also look at Ed's boiler choice FAQ:

http://www.makewrite.demon.co.uk/BoilerChoice.html

Thanks for the links. The fnal one is particularly valuable. Can anyone
offere any advice on choosing a boiler whose spares will be available (and
affordable) for a long time? (I realise that nothing is guaranteed..). Can
such a combi be got for under £800?

Al

(Andrew Gabriel) wrote in news:k2bdgf$64q$2
@dont-email.me:


When designing my system, I looked for the figure for heat
loss from boiler casing and couldn't find it, so I assumed
200W. This turns out to be wrong, due to the above. If it's
been on a very long time, there's a warm patch in the middle
of the front just near the heat exchanger, but it probably
amounts to only a few tens of watts max

Unfortunately, the kitchen where my boiler will be located doesn't have any
room for radiators. I wish I could pay less and buy an inefficient boiler,
so that the boiler itself would keep the room warm!

Al

On 08/09/2012 14:04, AL_n wrote:
(Andrew Gabriel) wrote in news:k2bdgf$64q$2
@dont-email.me:


When designing my system, I looked for the figure for heat
loss from boiler casing and couldn't find it, so I assumed
200W. This turns out to be wrong, due to the above. If it's
been on a very long time, there's a warm patch in the middle
of the front just near the heat exchanger, but it probably
amounts to only a few tens of watts max

Unfortunately, the kitchen where my boiler will be located doesn't have any
room for radiators.

Have you thought of options like kickspace heaters that go under kitchen
units (fed from the CH but usually with electric fan assist)?




--
Cheers,

John.

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

John Rumm wrote in
news

Unfortunately, the kitchen where my boiler will be located doesn't
have any room for radiators.

Have you thought of options like kickspace heaters that go under
kitchen units (fed from the CH but usually with electric fan assist)?

Until I read Owain's post (and yours) I didn't know they existed. They look
like a good possible solition... Thank you....

A

Owain wrote in
:

On Sep 8, 2:05*pm, "AL_n" wrote:
Unfortunately, the kitchen where my boiler will be located doesn't
have a
ny
room for radiators. I wish I could pay less and buy an inefficient
boiler
,
so that the boiler itself would keep the room warm!

A plinth mounting fan-assisted heater?
http://www.discountedheating.co.uk/s...ckspace-500g-f
an-convector-heater.html


Fantastic! I didn't know such things existed. Thanks for that...


A

On 08/09/2012 18:13, AL_n wrote:
Owain wrote in
:

On Sep 8, 2:05 pm, "AL_n" wrote:
Unfortunately, the kitchen where my boiler will be located doesn't
have a
ny
room for radiators. I wish I could pay less and buy an inefficient
boiler
,
so that the boiler itself would keep the room warm!
A plinth mounting fan-assisted heater?
http://www.discountedheating.co.uk/s...ckspace-500g-f
an-convector-heater.html

Fantastic! I didn't know such things existed. Thanks for that...


A

We have one in our kitchen and it's very good, undersized a bit but it
works OK on boost; make sure you size it so it can run on low (and
quiet) fan speed.

--
David

On Thursday, 6 September 2012 16:03:55 UTC+1, AL_n wrote:
I am planning a new central heating for my house which is a 3-bed semi.

There is currently only myself living here, but I may want to rent the

place out to a family at some stage. I need to decide between a combi

(sealed) system vs a conventional system with expansion tank.



Sited in my loft, is a Fortic cylinder with integral expansion tank. It

appears to have an internal coil (not in use), as there are two unused pipe

connections on it. I'm currently using the Fortic cylinder as an immersion

heater to heat my tap water.



I gather I'd consume less gas if I choose a combi, rather than a

conventional boiler. However, my experience of combis is that they are

expensive to maintain. I always envied people with older systems that seem

to require virtually no maintenance. Even slight leaks can be ignored in a

not-sealed conventional system, I gather.



Has anyone got any views on the overall cost (money + trouble) of

installing and running a sealed combi system vs. a conventional system?



Thanks for any advice...



Al

I have a Vaillant combi. It is a non-condensing one, one of the last before only condensing combis could be installed. I installed it myself. It has just developed its first fault after nine years of operation without any servicing or intervention.

This would have been a biggie though, as no hot water or CH was being delivered. The fault-funding flow chart arrived at the conclusion 'change pcb', which would have cost a good deal I reckon if it were not for the fact I'm an electronic engineer and tracked the problem down to an arcing relay, which I fixed myself. Still, nine years of fault-free operation isn't bad.

I took the cover off to inspect the burners whilst I was at it and it was clean as a whistle inside except for a collection of dead mossies. Nor did it have the sort of cover seals that need replacing. Vaillant aren't the top brand and are nor immune to problems but I would recommend them.

I do hear it's best not to buy a new model of combi when it comes out - problems can occur that they fix for later production models. Probably best to buy a design that is reasonably mature.