Boiler installation advice please - why two?

[motco]

Deva Link said:

How big is the house?

Thanks GBman

House size not easy to answer as it's technically a bungalow of c.1550 sq ft but has a full area basement (it's on a steep hillside and one end of the basement is underground) and garage of another 1600 sq ft in all but the garage isn't heated and the basement only sparsely heated. I don't know what output the installer was aiming at and the estate agent knows less than I do. Sadly the elderly widow owner went on holiday and didn't survive the experience so I cannot ask her who was her heating man.

[motco]

Martyn D said:

Looks unusual and "interesting"!
The zone valve is on the return, do you know what opens it up and does the boiler fire up with this zone valve in the closed position?
Is it a sealed system with an expansion vessel?
Others may disagree but if it was in my house it would need some attention!

I know very little about it but I am getting a full survey done soon and I hope to get access while that's going on so I can give it a look over. I cannot confirm whether the valve is on flow or return as I don't know the boiler schematic.

[motco]

fourpointsixgt said:

The zone valve will open and the l/h boiler fires up, therefore the r/h boiler will be hot water and be used all year round and t'other one comes on for the heating. I reckon!!!
BTW the boilers are Potterton profiles, now obsolete, but generally reliable.

Many thanks fourpointsixgt and everyone. The surveyor is on site on Monday and I will try to get in there while he's there to look more carefully. Glad the boilers are generally okay - my old Potterton floor standing one is more than 40 years old and still works well!