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