Clive Arthur wrote:

On 10/02/2018 23:06, Roger Hayter wrote:
Clive Arthur wrote:

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...

https://www.jtmplumbing.co.uk/heatin...ltecnic-valves
-c421/altecnic-caleffi-robocal-bottle-air-vent-p9592/s9594?utm_source=goog
le&utm_medium=cpc&utm_term=altecnic-caleffi-robocal-bottle-air-vent-15mm-1
5mm-15mm-502649&utm_campaign=product%2Blisting%2Bads&gclid= EAIaIQobChMIova
q7Zec2QIVzrXtCh1MZgwIEAQYBCABEgKf4_D_BwE

...or even...

https://goo.gl/2ctbUC

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

Cheers

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.

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

Cheers

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!


--

Roger Hayter