They're Hot at the top, Cold on the bottom (Therefore it isn't air, which would cause the top of the radiator to be cold & the bottom hot) I've blead the radiators, and they are all filled with water.
Does this apply to all the radiators or just a couple, probably downstairs.
If its the latter, then its probably corrosion from the inside of your system, collecting in the bottom of the radiators. This can be cleaned through by having a 'power flush' done by the professionals, or by getting a mate and isolating each radiator thats affected, taking it off the wall and giving it a good wash through with plenty of water While you are there you should drain the system and refill, using a corrosion inhibitor additive.
I have a similar problem at the moment, but am thinking of waiting til spring to sort it, as I dont really want to be without my heating for too long.
also a possibility is slow water flow...i.e. hot water dribbles in at one end rises to the top and heats the top up before slowly cooling and exiting cold fru the outlet. try turning the pump speed up or turning other rads down so this one has priority.
I like top posting...it makes sense. more sense than bottom posting...however daft the system is, generally I will bottom post...except in one shot answers like this was supposed to be.
Your system has sludge in it which has settle at bottom of radiators You can clean your system with many different types of manufactured products from B&Q always follow their guidelines on flushing system
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