Thanks for the replies and possibilities, i forgot to say actually that the pump was disconected briefly from the boiler and relocated slightly higher due to a kitchen extension, the boiler wasnt moved just the pump to enable the new kitchen units and ceiliing to be built was about two weeks...
My boiler over the past year has started making a howling noise and i mean hoooooooowwwwwwling, when i start the boiler up after a few minutes you can start to hear the howling start and then it continues till it it is a full on howling/whistling noise, this can continue for anything up to an...