Radiator heating up even though it's off

[Craigja]

hi,

We moved into our new house 3 years ago and had problems with the heating from the start. The original issue was that upstairs got hot and it was 45 mins later before downstairs heated up. This was eventually fixed after it was discovered that there was only a single feed and return pipe coming off the upstairs feed and return loops to heat all the downstairs radiators. The solution was to upgrade the feed and return pipes going downstairs to 25mm and to split downstairs and upstairs into separate zones by taking the downstairs feed from a new output of a zone valve. All was good or so we thought!
Now the radiator in my sons bedroom heats up even though I have switched off the trv valve(I also swapped the valve from another radiator in case this was the problem), I know it's plumbed correctly as I can feel the pipe going to the trv is a lot hotter than the other end which is obviously the return..... I'm thinking that return hot water must be going into the radiator and heating it up, this is the radiator near where the single original feed was going downstairs if that matters? What I'm wondering is, would a non return valve at the return feed end of the radiator solve this issue?

 

[dilalio]

Have you checked that the pin operates freely on the TRV valve?
It may be stuck open!
You'd also feel if the lockshield was backfeeding as it'd get hot.
There's a chance it could be convection, a single check valve on the return should be ok to try and see what results you get.
Check the pin on the TRV first.

 

[Craigja]

If I remove the trv, how easy should it be to push in the pin?

 

[dilalio]

It should have about the same resistance as opening a clothes peg, and it should pop back up when released! Manipulate it a few time with maybe a squirt of Wd.

 

[Craigja]

Just checked, can't push the pin down with my finger but if I use something to stop the pin jagging into me it moves about 2-3mm, I assum that's fine? Has about the same r distance as the clothes peg you mentioned