Bad circulation and air getting into radiators


Postby macaque » Wed Jan 30, 2008 4:52 pm

My initial problem was with a large downstairs radiator that does not get hot. It's the furthest from the boiler and the other 7 rads on the system are fine. I decided to drain and flush the system (I have 8mm piping) and took the offending radiator off to flush it out. It was mucky but not that bad. My fix didn't work.

If I switch my pump up from speed 2 to 3, the radiator gets hot but then the pump sometimes pushes water up into the header tank and air gets in. Within 24 hours I have 2 upstairs radiators almost full of air.

The pump tees into the feed pipe from the header tank via a valve. I assume this is some sort of bypass circuit. I've got the valve almost off in the hope that it would stop air getting in but it still does. Any ideas please?
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Postby htg engineer » Wed Jan 30, 2008 9:37 pm

If the radiator heats when the pump speed is turned up - then there's no obvious problem with the radiator, valves or pipework. No blockages etc.

Have you tried balancing the system ?

To balance - leave the pump on setting II.
Turn the heating on - then one by one turn down the radiators that do work. Fully close the radiator valve and open 3 or 4 turns. The 'problem' radiator should work now.

Hope this helps
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Postby macaque » Thu Feb 14, 2008 12:28 pm

Thanks for your help. I have got the pump back to setting II now, which stops the air getting in.

I have balanced my radiators, perhaps not perfectly, but I do get a better flow to my problem radiator now.
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Postby roger196 » Fri Feb 15, 2008 11:28 am

Have you remembered to put inhibitor in your system after flushing?
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Postby macaque » Sun Feb 17, 2008 8:18 pm

Yes, I put that it via the cold water feed. Thanks.
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Postby stevew » Sat Feb 23, 2008 11:13 am

I have a similar problem, after the heating has been on a rfew hours, the upstairs radiators are full of air and the expansion tank in the loft is actually overflowing. How is the air getting in, could it be the pump ?
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Postby roger196 » Sat Feb 23, 2008 6:23 pm

First stage is to turn down pump from setting 3 to 2. Let us know if there is any improvement.
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Postby stevew » Sat Feb 23, 2008 9:48 pm

I turned the pump down from 3 to 2 about 3 hrs ago and also bled all the upstairs radiators, before turning the system on again. A few minutes ago one upstairs rad was completley full of air and 2 others needed bleeding. Also I could see that the level in the header tank had increased again. The downstairs rads never need bleeding. I am also beginning to learn in which order teh upstairs rads fill with air.

After many freezing months this is now fixed, I put in a higher capacity pump which initially made the situation worse. I guessed it moved all the dirt in the system and compacted it all at the most restricted pipe. Finally we found a blockage in the pipe which feeds the water back to the boiler, cleared it out manually, then put 2 bottles of centinal 200 in the system, ran it and now its great.
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