"Al" wrote in message
. 4...
You may not have one, you may have two single port valves, or just one
- it depends on the install.

Looks like 2 single port valves:

"Appliance Components Limited Morortrol"

I'm struggling to understand how a failed valve is causing this problem,
but then again, I don't do plumbing ;-)

Thanks for the help so far,

Cheers,

Al.


Okay, here is how it works....

Your timer has two circuits, one for the Central Heating (CH) and one for
the Hot Water (HW)
Live goes into this timer, and when the timer decides you want CH or HW it
applies that live to the appropriate terminal (one for CH and one for HW)

You also have two electric valves - one valve controls water to your HW
cylinder and the other to your Radiators.

Both these valves are connected to the relevant terminal on the timer via a
thermostat (room stat for the CH and cylinder stat for the HW) so when the
timer AND the stat are BOTH asking for heat, the valve operates.

Now, so we don't end up with a closed valves and the pump on, the pump (and
the boiler) are connected to a little switch in the valves (in parallel, so
when either valve is operated, the pump and the boiler are turned on)

It sounds like one of the valves has stuck open, causing the pump and boiler
(The boiler will still cut in and out as it has it's own internal thermostat
so it only fires when the water temperature is too low) to stay on even
after the timer is not calling for heat (removing this from the wall proves
it is not the timer sticking on)

Now we need to find out what valve is causing the problem here.
I suggest you remove the timer from the wall again and leave it off for 30
minutes or so - this will remove the power from both valves so they should
both be off. After the 30 odd minutes, go and feel the pipes both sides of
the valves - the one that is sticking on will be hot both sides, whereas the
one that has shut off will be cooler.

If you can't see what valve is for what, then find your hot water cylinder
and feel the pipes going into the SIDE of this and see if they are hot.

You did say earlier "The CH pump is running continuously, and it's getting
hot in here!" witch does indicate it is the valve connected to the CH side -
But it doesn't do any harm just to check!

Let us know your findings!

Sparks...