My mother's heating system is a balanced flue boiler, with a cylinder
'stat, a three way valve, but the heating is only controlled by TRVs
with no room 'stat. The boiler is a replacement one, but I don't
think it's been wired up correctly. When the cylinder's 'stat is
satisfied, the whole system, pump and all, turns off, irrespective of
whether heat is being called for by the radiators. The three way
valve seems to be permanently centred (allowing hot water through both
circuits).

I have the diagrams for a room stat controlled system, but I can't
find one without room stat. Are the connections simply bridged as
though the room stat is constantly calling for heat?

I've managed to get the installers to call back tomorrow, but on the
'phone they are arguing that it's the three way valve (which wasn't
replaced by them), so I'd like a bit of ammunition to fire back at
them.
--
Hugo Nebula
'What you have to ask yourself is, "if no-one on the internet wants
a piece of this, just how far from the pack have you strayed?"'