One radiator remains cold!

8 Nov 2012
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United Kingdom
Having a bit of trouble identifying the cause of a cold radiator. Heating is an unvented system fed from a hot water tank. The two rads closest to the tank heat up very quickly, but then there are three more that heat up very slowly and a final rad that stays stone cold. I tried balancing the rads, no joy. Even closed all valves on the other rads and opened them on the cold rad, but still nothing. Have bled all of the radiators. One thing to note is that the feed to the rad at the trv end is piping hot, but the return end is stone cold. no heat in the rad anywhere. Any suggestions from anybody more knowledgeable than I?

Much appreciated,
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could be blocked return pipe. turn both valves off, drain rad by undoing tail nuts.loosen pipe nut on return valve spin it round and retighten. put a bucket under it and gently open it up. you should get a good flow out of it. if you only get a trickle when it is fully open you have a blocked pipe.

is it piped in plastic by any chance?
It could be a stuck pin on the trv, much easier to check/repair than a blocked pipe.
Have checked the trv pin and it's fine, it's all copper piping. Interesting thing, the radiator is hot at the point of entry on the feed side, but literally only the bulbous part that connects directly to the valve, there is no heat whatsoever going beyond that point. blocked return pipe could make sense, as there would be no flow. Then again I was wondering if there might be a build up of sludge in the rad?
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remove rad and flush it with a garden hose outside? if its a very small one, might be easier to buy a new one. :)

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