air in ch system

17 Sep 2004
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United Kingdom
The system is micro bore, with each rad seperately fed from a manifold near the pump.

When heating switches on, one bedroom rad sounds like it is filling up, as if it were half full of air. Bleeding it, either before or after heating comes on, just produces water.

Standing next to the boiler, every so often there is the sound of air rushing round, just for a short period.

A couple of other rads periodically produce small amounts of air when bled. There is also a virtical pipe next to the hot tank, with a screw at the top which I was told was an automatic bleed valve. I tried unscrewing this a bit and water, not air, came out.

Any thoughts?
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