BANG! BANG! Air stuck in hot water circuit of boiler.

[aww999]

Hi folks, I was hoping for some advice with this problem before I hire a plumber to come and suck his teeth at me. For the last three or four weeks, I can hear air banging around in the pipes when the hot water circuit turns on. We have a system where there is a big hot water tank upstairs with a heating coil inside it. The water in this coil is pumped around and heated by the boiler (downstairs). As soon as the boiler fires up, I can hear loud banging and gurgling for one or two minutes, which then stops.

The pipework for the hot water coil has a T-piece with a vertical pipe about 300mm long, and a bleed valve on top of that. That must be the highest point in the system, but whenever I open the valve I get no air out, just water.

The problem seems to be slowly getting worse, which is obviously worrying - do I have a leak somewhere in the system that is allowing air in? I have checked as much as I can see but there is no sign of water escaping. Any ideas on what to d next would be much appreciated!

[Ricky_M]

What state is the system water? What boiler is it? What sort of set up, fully pumped or gravity hot water and pumped heating?

It could be sludged up, does it make a kettling noise at all?

Check you have water in the Feed and Expansion Cistern or if it is a sealed system, check you haven't lost pressure.

Does the noise come from the boiler or the hot water cylinder?