Radiator Cold Goes Hot When Bled Then Cold Again

22 Nov 2007
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United Kingdom
Hi sorry if this has been covered somewhere but I couldn't find it.

I have 1 radiator that is cold and both pipes are cold too. If I bleed for a while (Sounds like water and air coming out) one pipe gets hot and the radiator starts heating up but the pipe with the trv doesn't get hot. Then when I stop bleeding the radiator cools down and goes cold as before and both pipes are cold.

I've took the cap off the trv and the pin seems fine. I've bled other radiators too and tried turning all radiators off apart from the cold one which is on full.

Any help greatly appreciate. Thanks
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i would say you have a serious airlock or maybe a blockage.
if its the pipe with the trv on thats not getting hot/flow try shutting the lockshield fully and open trv full then bleed the rad, if the rad stops flowing when bleeding then you know it has a blockage or airlock thats not shifting.
I have closed the lockshield and am bleeding again, It sounds the same as before, there is is flow and doesn't seem to be stopping, Should i keep bleeding till the flow stops then try reopening the lockshield?

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I would try opening both lockshield and TRV fully. I would then shut down all other rads on system. If I still didn't get heat flowing through I would drain and check that my valves were not stuck. I know you have done this but do it again and tap the TRV with a spanner. If you are fairly competent and brave and don't have a cream carpet put towels all round and cover everything, then pull out the pin with a pair of pliers. Water should shoot up in the air then push the pin back in.Take care not to splash youself as the water may be hot, wearing a rubber glove will prevent discomfort . Scary but it works.
if the flow was blocked then it would only bleed for a min or so.
the same on the other one closed etc if they both flow then open them again and try run the heating etc.

theirs no reason why it shouldn't work.
I tried bleeding with one valve closed at a time and doesn't appear to be a blockage. Both pipes still cold though when heating is back on. I guess it must be the TRV even though I took the top off and the pin seemed fine wasn't stuck or anything. Maybe I should try what past3bar said pulling the pin out! I'm guessing this makes sure its unstuck?
Maybe I should try what past3bar said pulling the pin out!
Not a good idea! Water could escape through the hole.

Are you bleeding the system when it is on? It's best to do it when it is off and cold.
See Agile's bucket test if I were you.
1. it will show whether either valve is faulty.
2. Have far better chance of removing any stubborn blockage
3. will at least identify which pipe is causing problem.

Can someone put up the link please. I don't know where it is and I don't know how to do it. :oops:
Is this rad newly piped up? or on an established system. If its new there's always the chance its piped flow to flow.

Have just noticed. Lockshield gets hot trv doesn't. Bi directional TRV needing adjusting for direction of flow? Old single direction TRV
Hi rojaca thanks for that. update. Yesterday both pipes were cold as I said until I bled out some water and then the lockshield pipe gets hot and radiator goes warm after quiet a while then lockshield and radiator go cold again.

Today however when the heatings come on the lockshield pipe is warm! Not hot but warm however radiator is cold and trv pipe still cold.

Could this just be HUGE amounts of air causing this? I have bled out about 15L of water so far.
I didn't see what type of system you have but I suspect it's open (with f&e tank). Check you've got water in it, I had one the other day where customer had same symptoms, ball valve was stuck!
If it's a sealed system check the pressure, 1 to 1.5bar cold.
Hi sorry, It's a sealed system i've been making sure pressure is good currently at 1.7 cold.

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