On 25/04/2012 22:26, John Rumm wrote:

Also don't ignore the possibility of using one combi to heat a cylinder
of water as well as being able to provide hot water on demand itself.

This is exactly what I specified for our extension, and was surprised
when the plumber said that it was a little unusual. Seemed blumin'
obvious to me. The combi-boiler provides direct hot water for the
kitchen and utility room (the boiler being about six feet from those two
taps). We have a mains pressure hot water cylinder which is placed on
the other side of the wall behind the master bedroom en-suite and
provides hot water for all the bathrooms/toilets. The end result is
that the majority of hot water usage - the kitchen and our shower - is
through the absolute minimum of pipework possible.

The house (a bungalow, 4 beds, two reception rooms and two studies) has
two main central heating zones. Furthermore, I also specified that the
two studies, which before my time were converted from the integral
garage and were plumbed with radiators on a branch of their own, are now
fed as a sub-zone of zone 1 (zone 2 being the bedroom end of the house).

This means that I could (if I got round to it) simply wire in a seperate
thermostatic control or timer/controller to enable the studies to be
heated if I am working at home in the winter without *any* of the rest
of the house being heated.

The system works by having a normally-open valve interrupting all of
zone 1 except the branch for the two studies. Therefore, the study
controller/thermostat can be be wired to activate the boiler and the
main zone 1 valve but also close the normally-open valve, thus
activating zone 1, but actually only heating the two studies.

So, if "Kent" has a large house and has a problem with the location of
the hot water, and is thinking about how to arrange the boiler/hot
water/heating zones, the answer is: you can do all sorts of things - but
to my mind the idea of having two seperate boilers is barmy!

Michael