On 10/02/2018 20:41, 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.Â* 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.Â* I can't see any way, but there are two air vent valves on
the inlet and outlet.Â* They look a bit like this...

https://www.jtmplumbing.co.uk/heatin...BEgKf4_ D_BwE


...or even...

https://goo.gl/2ctbUC

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

Cheers
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.