One of my radiators was moved. After being replaced, each rad in the house was checked for airlocks, but water came from each. When swithched on, the boiler (Potterton) started banging after a minute or two. I then checked the pump for air and some did escape. After this, the banging ceased - however, the boiler only runs for a few minutes - one of the pipes gets very hot - then it cuts out. There is a swishing noise which I assume to be the pump. Any ideas what the problem is - could there still be an airlock in the system - or is the pump damaged ?