jim coughed up some electrons that declared:

Tim,
May I ask how you went about spec'ing and finding a supplier for the
thermal store?

OK, it's been a long process.

A mate has one of the DPS units (www.heatweb.com based in Epsom, Surrey).

I've also looked at Gledhill and McDonald Engineers.

Pricewise, the DPS units seem very expensive for a copper tank, but the
prices I've been quoted do include all the pumps, mixer valves, auxilliary
heaters and paraphanalia, so I guess that stuff adds up (I've not broken
the price down).

The unit I'm looking at is a CXC-210-AH6ADA-XEJD which you can stick in to
the box near the bootom of their web page to get a schematic up (though I'm
still fiddling with options). Cost, quoted at around 1700 inc VAT. That's a
210 litre system.

A Gledhill BMA215 is around 1300 for a complete system, but lower water
capacity.

McDonald is the cheapest at 900 ish for a Thermflow 210.

DPS seem the most clued up to speak too and the flash designer does allow a
pretty custom system to be put together. They're happy to have a visit if
Surrey is anywhere near you. McDonald are Scottish and I forget where
Gledhill are.

The bit about a thermal store decoupling the new boiler lower output
temp from the existing radiators has caught my eye - just fallen out
with a "professional" after 1 day - so back to square 2!

What I'm looking to do is:

Direct heating of open-vented thermal store from boiler. Twin tank stats and
a bit of relay logic by me will provide a boiler call-for-heat signal.
Boiler will control the pump on the primary circuit.


Same water runs via a mixer valve (top drop the temperature) to the rads off
its own pump, controlled by the heating programmer/stats (multiple zones).

Another take off runs round a plate heat exchanger to provide mains pressure
potable hot water - this circuit's pump is driven by a flow switch on the
HW to taps circuit, so nothing to do here really - it's automatic.

I'll bung a solar coil in at the bottom, just in case I go for some panels
in a few years.

Also, I'm adding 3 x 3kW immersion heaters (code above shows 2, mistake) as
back up if he boiler's out of action. 9kW will go some way to providing HW
and heating a couple of rooms (any couple, by turning some rads off) and
it's a cheap option. These will be wired individually to 3 MCBs off one
isolator, which will be used to engage back up electric heating.

=====

What it gains me is:

No cold water tank (I don't have a loft as such and our mains water is
reliable).

Mains pressure drinkable hot water.

In theory, a simpler boiler setup where the boiler has the best chance to
run efficiently with a long full output burn (perhaps this is less of an
issue than it used to be, but it might make the boiler last longer).

I can run the rads and HW at different temperatures.

Solar input.

Cheers

Tim