Two of the eight radiators in my house get only lukewarm. All eight radiators have been bled. The inlet pipes to the two dodgy radiators are red hot so the problem appears to be with the valves. I have tried to loosen one of the valves by removing the plastic cover and then tapping the top of the valve gently with a hammer but there was no improvement.

I have read plenty of advice on the web about loosening the pin in the valve but this seems to be inaccessible.

Photo of one of the valves

Could anybody advise what I can do to get the radiators working?

  • what happens if you close the other radiators? – ratchet freak Jan 17 '13 at 20:54

A possible cause for your problem could be air in your radiator.

You need to open this valve (try "unscrewing" it) to see if there is air in your radiator. It's simple but it can be dangerous : when there is no air anymore (assuming it is your problem) you will get very hot water, possibly with some pressure, so be careful. Then tighten the valve again, wait ten minutes and see if there is a difference.

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  • there should be a bleed valve on the other side where it is safer to bleed the air out (with only a small hole to let water escape) – ratchet freak Jan 19 '13 at 17:23

That type of radiator typically has a bleed-valve at one top corner, a flow-balancing valve at one bottom corner and an adjustment valve at the other bottom corner.

You should open the bleed valve with the pump off and wait until all the air is expelled and only water is coming out. You can usually feel that the lower part of the radiator is hot and the upper part cold, the boundary rises as you bleed the air.

Usually the lower valves have white-plastic caps, only one of which can be used to rotate the valve stem - that is the valve that is used after installation to vary the output or to turn off heat in unused rooms.

The other valve is the one that is set by the installer to balance heat output throughout the house. You shouldn't need to turn it.

I'd drain the system before dismantling the valves at the bottom to check for blockages.

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