My mother lives in a council bungalow, the hot & cold tank are located in the loft & the water is heated by a gas back boiler. A while back we noticed the bedroom radiator was cold. Tried bleeding it but still cold, all the others were OK. Called out the council & without checking anything the guy that called said 'The system needs flushing'. It was flushed, still cold! Second guy came round & again without checking said a new radiator was needed. It was fitted & now it and others on occassion are cold. Some radiators are OK, others cold. I've bled each radiator & still no joy. The water in the taps is OK. The pipe leading to the radiator is hot but it seems once it gets to the valve it (the hot water) goes no further. Any suggestions please.
if the water to the radiator is hot and the water away from the radiator is completely cold (the other side valve) your valve is closed whether purposly or seized OR the radiator is full of air and needs bleeding.
There should be roughly an 11 degrees difference between feed and return.... ie the feed is hot and the return is hot, just not as hot!! (reflecting the heat emitted by the rad).
Check both valves are open, try turning off all working radiators to see if problem radiators work. If they do work this rules out faulty valves, blockages etc.
Then try balancing the system, open all wheelhead valves but only open lockshield valves a few turns.
If there's no blockages and it has all worked well before I would take a look at the pump, maybe it's not strong enough with age to cope with all the radiators. If not already - turn up to spedd III, if already on that setting, or still no luck - replacing the pump would probably solve your problems.
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