One Radiator not Working

3 Jan 2005
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United Kingdom
I have one radiator which is not working, and am now totally confused as to why!

Initially suspecting a faulty thermostatic valve, I replaced this and re-installed the radiator. Radiator cold.

Removed radiator again, and tested the thermostatic valve and return valves with a bucket under the end of each pipe. Water flowed freely when either valve opened.

opened the thermostatic valve (with radiator still removed) long enough to confirm that the water was hot.

Connected the radiator to the thermostatic valve, turned on the valve, and confirmed water flowed through the radiator into my bucket.

Re-installed radiator. opened thermostatic valve (only) and filled the radiator by opening the bleed valve at the top. Radiator filled with hot water. Radiator now hot.

Opened the return valve, and left for an hour. Radiator now cold! all other radiators in the house hot!

turned off all downstairs radiators (except the problem one) and turned heating up full. left for an hour - radiator still cold!

Can someone please help before I go insane?

It's as though the water from the return is at a higher pressure than the feed, and the return pipe is always stone cold!

BTW this radiator USED to work until about a year ago.
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Possible blockage?
Remove rad again and hose thoroughly thru all orifices. :D
When you closed off the other rads did you just turn the thermostatic to zero, this doesnt completely shut the valve. Try closing all the return valves on the other rads and see if you get any flow through the cold rad.
System may need balancing, let me know how you get on.
Thanks for your comments. I'm sure there is no blockage in the radiator, as I got water flowing through it by connecting it up to the feed sife only and watching the water come out the other end.

Yes I did only turn the thermostatic valves to zero on the other radiators. I will go back and shut them all off with the return valves (probably tomorrow, now) Will keep you posted!
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Connect your bike's exhaust to each pipe in turn and redline it? :D
Chis R: Like it!

Racket: Shut all the other radiators off completely, and after some gurgling, faulty one got hot!

Have crudely balanced the system by opening up the return valves of upstairs radiators 1 1/2 turns, downstairs 2 turns, and the ones in the downstairs extension 3 turns, or fully open. All return valves were originally fully open (previous owner!). All seems to be workng fine now!

Thanks to everyone for the advice
Most of the effective balancing happens in the first turn open of an ordinary several-turn rad valve. Somestime 1/8th of a turn is all you need!

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