One Radiator Cold - flow pipe cold

7 Nov 2010
Reaction score
United Kingdom
Recently had radiators replaced & all are working very well except 1 radiator downstairs which remains cold most of the time.
When all radiators in house are on full, it will eventually become warm after approx 15 mins but never gets fully hot.
Have tried turning all other radiators off to force heat to this one, but the radiator remains cold & very quickly this causes the combi boiler to overheat and reset.
Flow pipe to this radiator remains cold most of the time and is only warm at best. Radiator has been bled & also removed & flushed. It doesn't have a TRV.
It has been suggested that the system is powerflushed, however this was done when boiler was replaced 18 months ago. Any suggestions to avoid the cost ?
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have you checked both valves for flow and that they are operating properly ?
run each one into a bucket/bowl checking your getting flow from bothsides and the valves are operating fully.

you 100% sure rad is clear ie when you flushed it water entered oneside came out the other?
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Yes - confirmed these were all done successfully & rad was clear.

Radiators were all replaced but existing pipes weren't replaced. Could there be a partial blockage ? When water gets through to this radiator it's only lukewarm in the flow pipe not hot like for the others. Thanks
Yes - confirmed these were all done successfully & rad was clear.

Could there be a partial blockage ?

thats two conflicting answers
was it like before rad was changed ?
has it been like it since new rad fitted or only just happened ?
Sorry if appears to be conflicting - I don't have plumbing knowledge so am not familiar with how things work. Was just wondering if there could be an intermittant blockage in existing pipes. All the old radiators were poor and didn't heat well at all so not sure if this was like this before or not. Thanks.
you say the system was powerflushed but was it done properly.
whats the condition of the water etc when you changed the rads.

going on what you have said i'd be looking on the side of a restriction/blockage if it still fails to heat when the others are closed down.
hi All, assuming this was posted 12 years ago issue was fixed :D having same type of issue - 1 radiator was always luke warm, never hot as others. Boiler was replaced and it was still luke warm. I have opened fully lockshield valve, but now it is cold and never gets even luke warm. I have closed all others rads TRVs and lockshield valves and turned on the heating - boiler overheated and switched off. Should I remove rad and flush it with hose? As well while rad is off should I open a bit TRV and lockshield valves to a bowl to see if flow is ok? Thanks in advance for any help

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