kent wrote:

Thanks John for such a detailed and considered response. Our old boiler will have to replaced soon and I have been thinking about options.

Combi appealed because without stored water losing heat I figured it
would be more efficient.

However if 2 (or even 3) people wanted to shower at the same time I
didn't think that one combi boiler would be able to deliver sufficient
hot water.

This is a fairly standard 4 bedroomed house with gas central heating and
a gas fired stove, but all cooking appliances are electric.

heatloss from a sealed tank is neglible

I leave mine on 24x7

--
To people who know nothing, anything is possible.
To people who know too much, it is a sad fact
that they know how little is really possible -
and how hard it is to achieve it.