On 26/04/2012 21:12, kent wrote:
On Thursday, 26 April 2012 20:25:40 UTC+1, YAPH wrote:
On Wed, 25 Apr 2012 12:51:19 -0700, kent wrote:

Oh dear, I didn't mean to stir the s*** ! Does this mean I am unlikely
to get any rational answers?!

No, it just means you are likely to get some irrational ones ;-)

Multiple boilers in larger properties is quite a sane idea. Generally,
however, they are ganged together so that either boiler can run quite
efficiently at the lower output required for heating in spring and autumn-
ish weather, with both coming on together for winter loads. This also
gives a degree of fault tolerance as a fault in one boiler doesn't leave
you entirely without heating, and may not even be noticed in milder
weather. However the controls required (including a mechanism for
detecting that just one boiler has failed, before the other one goes as
well and you really don't have any heating!) is more complicated and/or
expensive.

Combi boilers aren't generally ganged though: in the larger properties in
which ganged boilers would be called for the hot water demand (e.g.
multiple bathrooms etc) is likely to be greater than even 2 combis
working together can supply.

However a 4 bedroom house isn't large enough to likely require more power
for heating than a single domestic boiler can supply (and if it does
you'd be better advised reducing the heat losses than adding boilers!)
Given that the hot water requirement is the critical factor then some
form of stored water system ('Megaflo'-type unvented, or thermal store/
heat bank) or just a storage combi (e.g. Worcester's Highflows) would be
more appropriate. If you are seriously concerned about backup for when
the boiler goes down a stored water system with immersion heater and a
few cheap convector heaters stored in the attic should do the trick.

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

The astronomer married a star

Well John it certainly has made for some interesting reading and encouraged me to look a few technical points up on the internet. The conclusion I have come to is that for our four bedroom house I just need a condenser boiler to replace our old regular one (making sure that the condensing pipe is not in a location where it might freeze up) and install an electric shower if we really do want three people showering at the same time! Any idea how much just replacing the boiler might cost (with labour, not diy)?
The idea of having combi's really came from my wife who wants the airing cupboard space!
Anyway, thanks to all for your comments and suggestions.

I use Thunderbird and I can't see how to fathom out word wrap issues either!

I recall a friend who's combi boiler went u/s before Christmas. The old
one was classed as non-repairable, or should we just say that a couple
of plumbers couldn't repair it as it's must easier and remunerative to
install a new one.

A simple boiler change 5 days before Christmas cost £1,600 on a boiler I
could have got for £500. So the idea of immersion backup and some
electric heating sounds eminently sensible.

Perhaps Adam will be here shortly to advise on power diversity rules
regarding 3 showers?

The thing is, combis don't cost much more than a conventional boiler,
and I would be tempted, if the plumbing was straightforward to have one
shower running of the combi + hot water for the kitchen tap. That call
is dependent on proximity and nuisance of time for hot water to run hot.