Apart from a solenoid that needed replacing and the occassional drop in pressure, my boiler has been working well. Recently I had a new bathroom put in, during this my mains tap had been replaced with a new one. Now, (normally when CH is running, but not exclusively!) when I open the hot water tap to wash hands or dishes there is a whirring noise that builds up like an aircraft taking off. Also the Demand and Water Heating lights flash erratically as it begins to bang. It last a few minutes then I either switch off the boiler or let it finish. I tried reducing the flow a bit, still does it. I switched off boiler and drained remaining hot water, it turned yellow and was full of bits of rubbish, before clearing up. Problem still persists. Can anyone help please? 
