How do I find my zone valve? Help and information on all topics relating to your central heating, air conditioning and ventilation issues.

[adamt]

Hi

My heating is not working but hot water is (and is unusually/dangerously hot). British Gas came yesterday and diagnosed it as a broken zone valve. But they couldn't see the valve and have told me to find it. (Too busy selling me powerflushes and new boilers to look properly?!).

It's not in the cupboard with the hot water cylinder, or in the kitchen near the boiler, so it's obviously in the wall or floor somewhere, but can anyone give me any guidance about whether it's possible to reason my way to it, or which places are more likely than others?
e.g.
is it more likely to be on the flow or return pipe from the water cylinder? which is which pipe anyway?
is it significant that the flow pipe on my bathroom radiator is warm but no other heating pipes are?
should I be suspicious of blaming this valve when I know he didn't test the control switch or the room thermostat?
etc.

I know this is all a bit unspecific. All i'm looking for is simply to boost my chances of finding it to better than arbitrarily pulling my house to bits!

[Kenj]

The Zone valve or motorised valve is usually in the flow pipe after the pump. The pipe work should then split in two, one 22mm pipe going to the HW Tank and the other to the radiator circuit.
Conversely the pipework may split in two after the pump, in which case there would be two motorised valves, one in each circuit.

The flow pipe is the hotter of the two pipes leaving the boiler. This is the higher of the two pipes leaving the heat exchanger on many boilers.

The motorised valve has a fairly short electric cable so should be no further than a few feet from the wiring junction box, usually near the programmer.

I cannot believe anyone would hide this in a wall or under the floor. Try following all the cables that go into the junction box.

"is it significant that the flow pipe on my bathroom radiator is warm but no other heating pipes are?"
I doubt this has any relavance, heat will radiate along the nearest pipes, and the airing cupboard is usually near the bathroom.

To help any further you need to suply more data.
Is it a sealed system or open vented (Header tank in the loft)?
Is the system fully pumped or gravity HW (28mm hot water pipes)?
What make and model number is the boiler?