FOlks

Quick boiler question...

I currently have a Saunier Duval combi boiler installed in my house.
The install dates from 1987, i.e. before I lived there. It has been
running fine, although possibly not terribly efficiently of late (my
perception).

At a recent routine service, the engineer (the same company as I've
used for some years) says that the boiler will need some fairly major
parts replacing: heat exchanger, pump etc, which will cost a few
hundred quid. I was expecting this. He then looks at the pipework
leading in and out of the boiler, and tells me that it is actually the
wrong size (15 mil instead of a larger size- maybe 22mil?) and points
to the various step-down pipe adaptors fitted there to enable just
that fact. I actually knew about this already, since another engineer
from the same company had told me the same thing some years ago, so I
am not too surprised to hear it again.

My question is this. Is the wrong size pipework a major problem;
should I have the current boiler repaired or should I have it
replaced, and in the latter case, would I have to have a condensing
boiler fitted rather than another combi? I believe there are new
regulations about boiler efficiency coming into force next Spring?

One more thing. Bear in mind I will probably move house next year.

tia
Dave P

On 16 Apr 2004 05:22:43 -0700, (Dave Phillips)
wrote:

FOlks

Quick boiler question...

I currently have a Saunier Duval combi boiler installed in my house.
The install dates from 1987, i.e. before I lived there. It has been
running fine, although possibly not terribly efficiently of late (my
perception).

At a recent routine service, the engineer (the same company as I've
used for some years) says that the boiler will need some fairly major
parts replacing: heat exchanger, pump etc, which will cost a few
hundred quid. I was expecting this. He then looks at the pipework
leading in and out of the boiler, and tells me that it is actually the
wrong size (15 mil instead of a larger size- maybe 22mil?) and points
to the various step-down pipe adaptors fitted there to enable just
that fact. I actually knew about this already, since another engineer
from the same company had told me the same thing some years ago, so I
am not too surprised to hear it again.

My question is this. Is the wrong size pipework a major problem;
should I have the current boiler repaired or should I have it
replaced,

At that age, it is nearing the end of its useful life. I wouldn't
spend several hundred quid on it.

In most domestic installations, apart from ion large properties, 22mm
at the boiler flow and return is normal and adequate. Below this,
the flow rate through the pipes becomes inhibited and it's difficult
to transfer the heat. To some extent the pump deals with this, but
to mode the same volume of water, it has to flow faster and more
noisily. Beyond a certain point it's not really possible to go
further. In short, the pipes from the boiler and forming the main
trunk to the radiators should be in 22mm up to a point where enough
branches to radiators are done to bring the flow requirement to a
sensible level.




and in the latter case, would I have to have a condensing
boiler fitted rather than another combi?

This isn't the decision.

You can have boilers without combi function that heat radiators and a
cylinder or you can have a combi. Separate to that, you can have
condensing or not in both types (i.e. 4 main permutations) Actually
there are more, but this is the essence.




I believe there are new
regulations about boiler efficiency coming into force next Spring?

It has been mooted that the minimum SEDBUK efficiency will be raised
to 86%. This is not achievable with the typical 78-80% conventional
boiler of current manufacture. Whether that happens before next
Spring is not completely clear, but it is the aim.

It is beneficial to get a condensing boiler anyway and yes you can get
a condensing combi.




One more thing. Bear in mind I will probably move house next year.

You may prefer to get a cheap non-condensing combi in that case.



tia
Dave P

..andy

To email, substitute .nospam with .gl

He then looks at the pipework leading in and out of the boiler,
and tells me that it is actually the wrong size (15 mil instead
of a larger size- maybe 22mil?)

IIRC, 15mm is good for around 6kW, which will just about run a flat or a
well insulated small house. Should the official requirement be greater than
15mm, it won't just stop working, but may get a little noisy, as you'll have
to turn the pump speed up to compensate for the losses. This causes the
water to rush faster and may disturb the smooth flow of the water, causing
greater amount of noise than may be desiried. Provided that all the
radiators heat up well, even in the depths of winter, and the noise isn't
too bad, there is no real need to go repiping.

would I have to have a condensing boiler fitted rather than another
combi?

Not yet, although they are usually recommended. Also, as condensing boilers
are typically designed for a greater temperature difference between flow and
return, they can shift more power into the same size pipe runs, so may
alleviate the pipe sizing issues, particularly if the radiators are
oversized, allowing a 70/50 system, instead of the conventional 82/70.

You may be getting confused about the term "combi". The "combiness" of a
boiler is unrelated to its condensing nature. You would need to replace with
a condensing combi boiler. However, as you are moving out soon, you may find
it financially more beneficial to pick some cheap bottom of the range
traditional combi and hope it lasts until you move.

Christian.