One cold radiator

15 Jan 2008
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United Kingdom
Hi all,

I've just had a leak on my gravity fed central heating system so have had to drain the system. While I was doing so I thought I'd take the opportunity to completely drain everything, flush it out, run some cleaner through, and then re-dose with inhibitor. First two steps are now done (drain and flush) and I've refilled and added the cleaner which the bottle says is best to now leave in, with the heating on as normal, for two weeks.

I have 7 radiators in total, 2 downstairs and 5 upstairs. I re-filled the system and have bled the air out of all the radiators and they are all working fine, apart from one of the downstairs radiators which is stone cold. What seems even more odd is that, after fixing the leak, I re-filled the system at that point, temporarily, and at that point, they were all working apart from one of the downstairs radiators, but that time it was the other one - which is now working fine.

Any suggestions as to what is causing this and how do I fix it?
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turn off ALL the hot ones.

Which cleaning chemical are you using?
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you can do that to each of the radiators in turn during the cleaning phase, have just one open at a time until it quickly heats up all over (including the middle, and the bottom rail).

The flow from a circulating pump is not very forceful, but this will concentrate the flow through that one radiator and improve the cleaning effect.

Once they are all back in operation, you can Balance them using the Lockshield valve so they all heat up at about the same rate. The principle is to reduce the flow through the rads which take most of it, so that some flow is forced to go round the more distant, or difficult radiators. You may need to rebalance again after cleaning has shifted some of the sludge.

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