In an earlier contribution to this discussion,
Martin Pentreath wrote:

Now I know I'm on dangerous ground here, and I really don't want to
unleash combi war, round 481, but I would be interested in answers to
this.

I have a combi which works very happily - an Ariston Microgenus 27kW.
It's a perfectly good combi, but I'm toying with the idea of having a
pressurised cylinder installed to provide for stored hot water at
mains pressure. Before I get Mr Plumber in to suck his teeth and
declare the whole system to be in need of ripping out, is there any
reason why the combi can't be used to provide stored hot water in this
way? My primitive understanding of combis is that they are
conventional boilers, with an additional heat exchanger bolted on
which provides the hot-water-on-demand function. Presumably my scheme
would render the secondary heat exchanger redundant and I would just
be using the primary heat exchanger to provide central heating and hot
water as a conventional boiler would. Is this about right?

Martin

Yes, it is perfectly feasible to use the CH side of a combi to power both
the CH *and* stored hot water. You will need some sort of zoning control
(either a 3-port mid-position valve, or two 2-port zone valves) in order to
have independent control over the CH and stored HW.

In order to provide stored hot water, you can use a conventional indirect
cylinder with a header tank, or a mains-pressure unvented cylinder (which
must be professionally installed) or a thermal store/heat bank system - you
pays your money . . .

Many people who do this sort of thing continue to use the original HW side
of the combi for providing instant hot water to the kitchen sink - and use
the stored hot water for baths and (maybe) showers.
--
Cheers,
Set Square
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