Why are my radiators warm when heating is off?

[mistressploppy]

Only occasionally, one or two of them seem to come on, despite the heating being off. Why is this? It's quite an old system, I think (moved in several months ago)

Do they get properly hot, or just a little bit warm?

They can sometimes get a bit of warmth just because pipes run alongside hot-water pipes and the warmth works its way along.

But if they are actually hot, its more likely that there is something not quite right in your system - possibly a valve not closing properly, or even that changes in the overall system have ended up with something connected that shouldn't be.

We had a system where radiators had been added, then more, then more, then there was a change so there wasn't a filler tank in the loft any more - end result, 2 radiators very hot whenever the hot water was on, because there was an odd pipe joining one bit of tangle to another bit of tangle. Took them a lot of head-scratching to work it out!

Valves are the other possibility - the hot water from the boiler may be only meant to go one direction when your heating is off, but if the valve is stuck slightly open then it may go to the radiators as well.

Unfortunately, you probably need an engineer to come and take a look at the symptoms.

Thank you, that's really helpful

easy peasy

unless it is very old, it will be a fully pumped system. If either the hot water cylinder, or the room stat, calls for heat, and the timer is on, the stat opens a valve, the valve turns on the pump and the boiler.

If the pump is running, and the electrically-operated valve is worn out, or faulty, them some of the pressure from the pump will cause heat to go where it is not needed

These motorised valves have a brass part, with a rubber ball inside, which wears out, and an electic motor inside a metal or plastic head. On modern ones you can change the two parts separately. It is more trouble to change the brass part because you have to drain or bung the water, but it can be worth changing the head only if that is where the fault is.

The valve will usually be next to the pump and/or boiler and/or cylinder

usually like this

Start asking around for a well-recommended local plumber. As it does not involve opening up the boiler he does not need to be gas-safe registered, but can be.

It is a very common repair

Thank you so much, Piglet