Air Vent Valves

Our pressurised central heating boiler is making rattling/banging noises, but only when the hot water is on but not the radiators. It sounds like air in the system; all the radiators are bled.

So I wondered if there was a way to bleed any air from the hot water tank coil. I can't see any way, but there are two air vent valves on the inlet and outlet. They look a bit like this...

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...or even...

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On ours, the plastic cap/button is screwed down tight. I think it should be loose. Should it?

Cheers

Reply to
Clive Arthur
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Yes, on ABVs the caps should be loose, but it's highly unlikely to be air in the coil. If the problem really is only present with hot water on then it might be the zone valve or some other valve rattling, or a tap jumper rattling if the it isn't completely off.

Reply to
nothanks

Yes, the button should be turn and a half or so open to let out air. But don't leave them open after all the air's gone. In theory that should be a good idea, but in practice they get gummed up with limescale, leak water and don't let air out any more if you leave them open too long.

Reply to
Roger Hayter

Or insufficient flow through boiler so it's kettling or boiling.

BTW, ABV's mustn't be left open, or they will form hard water scale on the seal, and then fail to seal and leak water.

Reply to
Andrew Gabriel

Thanks all, that seems to have worked. I'll close them now.

Cheers

Reply to
Clive Arthur

That's interesting. I've always left them open and not had a problem with scale, but I take the point.

Reply to
nothanks

I suppose the limescale problem is actually going to depend on your local water hardness and on how well inhibited and leak free your CH system water is. I can only speak from my experience, but I note others say they leave them open!

Reply to
Roger Hayter

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