Thanks for the good point challenging the idea of replacing the old
boiler with a combi. With the thermal store, system as I understand
it, the boiler is simply a source of heat to top up the thermal
store.


I also meant to write further, but Windows "sticky keys" got me. If
you have never experienced that, consider yourself lucky.

Anyway.

The thinking behind installing a combi boiler was to achieve instant,
*mains pressure* hot water. The hot water in the house *is* hot (yes,
I have fallen in love with the simple, little to go wrong, 25-year old
boiler). Now, the thermal store literature claims it can deliver
instant, *mains pressure* hot water. I can't understand *how* , since
it's just a cylinder - sorry, thermal store. Won't it need a head of
pressure i.e. loft installation to deliver hot water under pressure?
I'll take that on trust unless anyone can explain how the thermal
store system achieves the mains pressure output?

I can now see that my requirements for heating and hot water are
contradictory. I guess the thermal store approach tries to gather as
much usable heat as it can for both needs to reduce gas (or other
fossil fuel) burned. This thread is helping me understand the options.

BTW, I have looked at that self-built heat-exchanger to reclaim heat
from shower waste and pre-heat the cold supply to the shower. Looks
really neat, simple to manufacture and plumb in - so seems surprising
it's not mass-produced.

Clive