Temperamental radiator?

[Mojo]

Hi everyone
I am more than happy with the heating in my 3 bed semi - have TVRs on rads and they all do what they're supposed to. Have a mystery though with one of the upstairs rads (in a cold bedroom). When heating comes on in the morning, it heats up and then goes off too soon. In afternoon, it heats up and stays on until room reaches temp. Heat had just come on and all rads are piping hot so it doesn't seem to be a case of all rads not wanting to be on together. Sorry if this is a stupid question - I try my best but I'm not a plumber and to make it worse I'm a girl (apologies to all feminists!)

Sorry - update to above - rad has just gone off having been on for about an hour and room not up to temp, It normally stays on in the afternoon. Dont suppose this makes any sense.

Further update - it's now red hot again! It's the only rad that's doing this 'on and off' thing. Is it a case of because it's the last rad on the system (I think!) it's having to 'share' the water until everywhere is hot?

 

[Cds]

This is probably down to balancing in that the offending radiator is not getting enough of the flow.

Does the system have a room thermostat? If so this is probably shutting the system down before the room with the troublesome radiator is up to temperature.

Is the room in question subject to higher heatloss than other rooms? i.e. more external walls than other rooms or over/next to a garage?

To prove that the radiator is man enough shut down the TRV’s on all the other radiators and turn the room thermostat up to maximum. If the room gets warm then it’s a balancing problem if not the radiator might be undersized.

 

[doitmyself]

If the rad is either on (hot) or off (cold) its almost definitely due to the system not balanced properly. TRVs are not like switches, they are more like the accelerator of your car, they control the flow through the radiator.

If the balance is incorrect they will tend to act as on-off switches.

 

[Mojo]

Thank you, both. I think it probably is the balancing as I've just noticed that the bathroom rad is going on and off too. The two rads in question are in very cold rooms with alot of heat loss.
The room thermostat is high so it hasn't switched off, so it's not that. Should have mentioned too that the lounge rad is really toastie and doesn't turn off until temp in lounge is about 22.5 (on setting 3). Suppose this is a plumbing job as it's not within my skill base. Mind you, you certainly keep warm running around and feling the radiators!

 

[doitmyself]

Why not have a go yourself - you can't make it any worse than it is.

Detailed instructions are here

If you don't want to go to the bother of buying thermometers, just go by feel. The return pipe should be cooler than the flow. Use the boiler pipes as a guide.

If that doesn't improve things, call in a plumber. But if the plumber tells you that you don't need to balance radiators with TRVs, don't employ him!

 

[Mojo]

Thank you again. I've been out for a coule of hours (got bored with feeling radiators) - have just come back in and the two suspect rads are really hot - house is lovely and warm Would they get hot at all if it was a balancing problem or would they be cold all the time?

Sorry - I've just realised that you've already answered this question in one of your posts above. Think I'll make this 'the last post' - ha! ha! - as this must be getting boring for anybody who knows anything about central heating. Good night and thank you.

Sorry - I've just realised that you've already answered this question in one of your posts above. Think I'll make this 'the last post' - ha! ha! - as this must be getting boring for anybody who knows anything about central heating. Good night and thank you.