Are you sitting comfortably? Then I'll begin - this is a real saga!!!
I live in a terraced house and have a very old CH system which generally works quite well. However there is one problem - one radiator never works and is always cold. All the rest get hot immediately. I actually replaced it with a new radiator and newly fitted TRV to se if that would solve the problem but it didn't. The old radiator had always been cold but I was told that it had worked well at one time.
The pipe under the lockshield gets very hot when the heating is on. I have tried bleeding the radiator until water comes out. I have tried turning all the other radiators off and then put the CH on to see if this one radiator would work but to no avail.
I have tried tapping the TRV and remving it to ht the pin which moves and is new anyway so should be okay!
I have tried turning the lockshield off and putting the TRV on full and then bleeding the water out based on advice received from a plumber. Whilst doing this the pipe under the TRV got hot and for a very short time the top of the radiator got very faintly hot but the bottom remained stone cold. After emptying seven basins of water I gave up trying to drain it further.
I am really at the end of my tether now with this as it is obviously winter, my living room is cold and I have paid for a radiator that doesn't work!
Please can anyone help me. Is it a balancing problem?
Sounds as if the pipework to the radiator is partially blocked. This could be with sludge or even an airlock. To find out and clear it, turn off the valves and disconnect them from the rad. If the pipes don't move you need to remove the rad. Using a short length of flexible hose, connect one end to one of the valves and place the other end in a bucket. Open the rad valve fairly wide. Run until the water runs clear or air is expelled. Repeat for other valve.
I came across this exact same problem last week, and here's what sorted it for me:
shut both valves, take rad off, open both valves in turn to find which side is blocked, trace this pipe back to joint that tees off to another radiator ( I had to remove some skirting board and boxing in). Drain system and de-solder this joint.
If problem is same then this joint will be blocked, hence, replace.
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