The Range Cylinders models are reasonable. Christian is pricing them up
right now. I think he is going that way.

Nah. I've gone for a 180 litre indirect DPS Pandora fed by a Bosch Worcester
Greenstar 28HE II System installed in the loft on a Honeywell 'S' plan,
zoned for water, upstairs, downstairs and conservatory. The conservatory
might be wet underfloor or forced convection radiator, but haven't decided
yet (or even built it). The loft is already boarded, with lighting and
mounted loft ladder, so it is a practical place to put it.

My biggest fear with the heat bank is that drawing water will kill the heat
stratifiction, leading to hot water reducing below 55C when there is still
energy in the system. I'm hoping storing 180L at 75C will overcome any such
problems. My water is hard as nails, so the removable external heat
exchanger able is a big plus that can be stuffed with Viakal or replaced as
required.

Christian.