Hi, I've got a glow-worm boiler which is about 7 years old. A few minutes after the flame comes on, it starts making a loud whining, howling noise. I can hear the noise loudest when I put my ear against the boiler. If I have the boiler set too high it sometimes bangs and shake the pipes quite violently. So I've got the boiler set on minimum so it doesn't get too hot, which seems to help. I've got my pump set on medium which I believe it should be for a smallish house. Setting it lower makes no difference. The header and feeder tank (float etc) seems to be working OK - I took a look and it seemed like there was probably enough water in there, and the float seems to work.
I'm suspicious of air getting in because the radiators need bleeding far too often, and when they are bled, it does reduce the problem. However the problem very quickly comes back within about a day. I'm also wondering whether there could be scale buildup in the boiler and whether it's worth buying some cleaner to put in the feeder tank, just in case. I can't see any leak or water dripping anywhere, although I can see greenish deposits in the airing cupboard so there may have been a leak there in the past.
Should I buy cleaner for the feeder tank, and what more can I do to accurately diagnose the cause of the problem?
I'm suspicious of air getting in because the radiators need bleeding far too often, and when they are bled, it does reduce the problem. However the problem very quickly comes back within about a day. I'm also wondering whether there could be scale buildup in the boiler and whether it's worth buying some cleaner to put in the feeder tank, just in case. I can't see any leak or water dripping anywhere, although I can see greenish deposits in the airing cupboard so there may have been a leak there in the past.
Should I buy cleaner for the feeder tank, and what more can I do to accurately diagnose the cause of the problem?

