Boiler airlock? Or loose pipes?

Hi all,

I've been trudging the net trying to find a solution to this problem. I'm pretty handy so willing to have a go myself if anyone has any advice.

We moved to a new house in October, and as the weather got colder we've noticed a violent banging coming from the central heating when it fires up. We can track the banging from the attic down to the boiler. When the banging reaches the boiler, it stays there for a minute then disappears - then nothing more until the next time it all kicks in. The boiler is a potterton suprima 40L.

I've tried bleeding the radiators, went to find a pump to bleed but can't even tell how to take the covers off to get to it.

I'm not sure if this has something to do with loose pipes banging as they expand, or if it's an airlock. If it's the latter, where would be the best point to try and bleed?

Thanks in advance for any suggestions or assistance.

Kris

Violent banging you say- what, like someone hitting the pipes with a sledgehammer? Or is it more a creaking ticking noise-audible and irritating but you can hear the telly over it?
If the latter then it is almost certainly expansion noise from pipes that are clipped or notched too tightly, or where there is a long straight run with a rigidly fixed point at each end.

Thanks for your reply.

It's the sledgehammer version. We do get odd bits of trickling, but I the banging is the main concern. It's still an old tank system, not a combi. Didn't know if that was obvious or not with the boiler type.

I'm not sure about straight runs, as the banging happens in 2 or three places on each wall/ceiling.

Time for some floorboard lifting then, pick the easiest one to get to first, lift the boards and see what's what. Favourite noise generators would be where there are straight runs between joists then elbows through joist notches or holes with the notch/hole having no clearance for expansion (a metre of copper will extend by about a millimetre on heating from 20 to 80 deg c). Don't enlarge notches/holes too much, they have to support the floor!

it sounds to me like your boiler could be overheating and the water is boiling inside. violent banging like you're describing isn't usually pipes expanding.
go check your F&E tank (the smaller one of the two) in the loft when it's happening, is the water really hot? is there any water in it at all even? is the boiler still firing when its banging?

take a video and post it along with some pictures, that would really help