My boilers banging away. The system's been cleaned, drained, flushed,
bled 2 or 3 times and had a new pump fitted and tried on all speeds,
but still the boiler bangs away. I think it's air, in the system, I
can hear it whooshing around the boiler and through the pump. The
system's about 9 years old and has been working fine since I inherited
it about 6 months ago. The banging became increasingly worse over a
few weeks. Once drained and filled and the radiators bled a couple of
times, no further air builds up in the radiators, so I don't think air
is being drawn into the system once filled. It's more like trapped
wind!

Close to the pump, I have what I think is an air separator. It's a
cylindrical object (about the size of one of those enamelled tin mugs)
with 4 ports. The pump seems to circulate water between 2 ports on one
of the flat ends. A 3rd port at the opposite flat and 4th port coming
off the top but off-centre both go up into the loft to the header
tank, one to the header supply, the other to an open vent. If this
thing is an air separator, then it's not working as you can also hear
the air whooshing through the circuit.

Can someone confirm it is an air separator and do they fail? It's been
painted and there are no visible markings. It looks different to the
separators I see around the plumbing/heating supplies, has this design
been superseded in recent years? Any idea where I might get a
replacement? Any other ideas about the problem?

Thanks in advance,
Russell