On Sat, 04 Sep 2004 23:03:38 +0100, Set Square wrote:

In an earlier contribution to this discussion,
Ed Sirett wrote:

On Fri, 03 Sep 2004 21:13:00 +0100, Set Square wrote:

In an earlier contribution to this discussion,
Jentrev96 wrote:

i would like to replace my conventional boiler with a combination
boiler has anyone got inst instructions ?please

Others have already commented on competence issues related to gas
fitting - so I won't repeat all that.

However, I'm faced with the question "Why would anyone conceivably
*want* to replace a conventional boiler with a combi?"

Are you *sure* you want to do this, and have considered all the
implications?


To parody Fowler on the subject of split infinitives:

The combi questioner can be divided in several groups.

Firstly, those who neither know nor care.
These are the happiest of all especially if someone else pays the
bills.

Secondly, those who don't know and do care.
They post to uk.d-i-y.

Thirdly, those who know and always approve.
We all know who he is.

Fourthly those who know and always condemn.
To those of you who are in this group I beg you to read on. I suspect
that this group is larger than it might otherwise be on account of two
factors. Firstly there are a proportion of professional installers
who for their own reasons prefer to always fit a combi regardless of
the needs of
the customer. Secondly those in the third group whose style of
advocacy could be described as abrasive.


Fifthly those who know and discrimate.
There are quite a number of criteria which have to be considered.
User's infomred preferences.
User's previous experience.
User's prejudice.
Size of dwelling: Space v. cylinder benfits.
User's HW usage patterns.
Instant Availability v. Storage heat losses.
Number and size of simultaneous or back-to-back HW demands
(Showers v. baths.)
Quality of mains supply.
Pre-Existing arrangements and cost implications.
...

I'm not sure into which category I'm deemed to fall, having questioned the
wisdom of converting to a combi!

Although I have a bias against combis in principle, there are circumstances
where they are appropriate - when starting with a clean sheet. For example,
my 95-year-old father-in-law lives in a bungalow which is heated by electric
storage heaters, with the hot water being heated by an immersion heater. I
would desperately like him to ditch the storage heaters and go for a decent
gas-fired heating and hot water system. [Gas *is* available, even though he
doesn't currently use it]. A combi would suit him down to the ground.

However, in cases where a system already exists - using a conventional
boiler and stored hot water - there would, in my view, have to be some
pretty exceptional circumstances to warrant converting to a combi-based
system.

A typical dwelling where a combi might well be the best approach is:

A 1 bed flat built in 1975 which has a Arcopack (sp?) and a life expired
conventional boiler.
The Arcopack unit is pre-plumbed steel contraption with a steel CW
cistern and an insulated copper HW tank/cylinder) in the lower section.
Typically a small F&E header tank is provided inside the upper part of the
cistern for the primary circuit.
Flow rates to the bath are moderate and there is no (I don't mean little)
pressure for a shower.

The mains is plastic but only 1/2"/20mm. Good enough for a combi but
debatable for unvented.

The cupboard space is relatively more valuable in a small flat. The
maximum occupation is likely to be a couple + very small kid.

You will not likely rent out any such flat in the middle market private
sector without a shower.

The combi will only be a little larger than the old boiler.

Booster pumps can cause noise problems leading to serious conflict between
neighbours.

The case for a combi is fairly strong in the above scenario.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
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