Central heating wants to be on all the time.

The hot water circuit responds to the timer, will only feed the coil in the tank when it’s told to.

But unless the boiler’s switched off, the central heating will be on, whether the panel is saying it should be on or off.

I’ve tried talking the control panel off the backplate, and the same happens: hot water off, CH on.

The thermostat relay clicks when I turn it back and forth over the current temp, so that seems to be working fine too.

So where’s the problem? What’s telling the boiler to fire and feed the circuit when everything should be off?

Cheers for any help, and please don’t assume I know very much, or even anything about boilers and central heating!

Have you got an external frost thermostat that is misbehaving so it is permanently in frost protection mode? See if there is an information display that will tell you what it thinks inside and outside temps are

I think we had this when we first moved into our current house – 9 years ago so a bit wooly, but I think it was caused by the motorised valve in the airing cupboard being stuck. I can’t remember why it caused the heating to stay on, but it did…

New valve sorted it; or it might have just been a new motor on the valve.

Some Googling seems to corroborate this.

EDIT – some of them have a manual over-ride lever – if yours does you might be able to fiddle & see if it solves the problem. If it does, then get it replaced.

don’t assume I know very much, or even anything about boilers and central heating

Same here but assuming it’s a combi boiler is the the triple valve (thing that switches between the 2?)

Have you got an external frost thermostat that is misbehaving so it is permanently in frost protection mode? See if there is an information display that will tell you what it thinks inside and outside temps are

Pretty certain there isn’t one of those. No temp reading on the control panel, no mention anywhere of frost protection. And when the control panel is taken off, the boiler still fires and the CH is on.

Edit. That was the only reply when I slowly started typing!

Cheers, I’ve been thinking and googling at the same time, and got to the valve.

Funny how pulling your thoughts together to ask something on here triggers a bit more thinking!

Any way of checking valve operation without replacing it?

The valve usually has a lever to override the “off” position to an “on-for-both-heating-and-water” position but not the other way around.

However, when the heating goes off, you should be able to hear the thing close by spring action. If it’s not doing that then it is probably stuck.

Microswitch in a diverter valve stuck on?

Any way of checking valve operation without replacing it?

Is there a way of manually overriding it?  We had one system that was running too hot where it was just a valve that had stuck since it was last used back in february.  Manually opening and closing it fixed it

Mind you that is a valve on the heating in a system in a big building so it just had a big lever to pull.  No idea what it looks like on a home boiler

There’s a manual override to open, but there’s no resistance like on the HW valve. So it seems like that’s stuck open, causing the permanent call for hot water.

Don’t know if there’s a way of unsticking it, or whether I should just swap for a new one. It’s a Honeywell V4043H. Back to Google…

I would say motorised valve not fully closing.

If you have 1 for hot water and 1 for heating, you could swap the wires over to see if it still does it.

Failing that, just buy a new one for £40 odd. Even if it isn’t the valve this time, it is bound to fail at some point so handy to have a spare. If you get the exact same model you can just change the head so no need to drain down the system.

Find your wiring centre.
Have you got one valve or 2?
Then find your CH valve. Trace the cable from the valve to the wiring centre.
Turn off at the fused connector. remove the orange wire, from the valve to the wiring centre, at the wiring cnetre, put in in a connector block to be safe.
Turn the fused connector back on, turn off the HW. Turn off the CH.
The boiler should do nothing, apart from its usual start up sequence, which can mean 5 minutes of the pump running etc, depending on what boiler it is.
If it does nothing, turn off again, put back in the orange wire.
Turn on, but leave the HW and CH off.
If the boiler now fires up with the CH on, then it looks like the valve head needs replacing.

There are other things that coudl be wrong, but if the timer and the thermostat are off, then it is likely to be the valve.
They are usually a quick swap, as the heads can be changed on their own for the majority.
What make/model of valve?

Stuck CH valve. Popped the valve box cover off, popped the cover off the Synchron motor, literally just touched the motor, and it whirred back into place. Everything working now as it should.

Thanks for your help, everyone!

Awesome

Stuck again, got another motor from Plumbase round the corner for 9 quid, all good again!