Had the pump replaced on my boiler which is a year old and there is now an irritating low level hum coming from one of the pipes. Boiler is in an upstairs bedroom and pipes run down to living room below and are behind a hardboard partition. I assume the answer will be get the bloke back in but is there anything obvious that’s safe for me to check first? There is no air in the radiators and the humming occurs as soon as the heating or hot water is turned on. When I have checked upstairs where the boiler is the noise isn’t so bad and doesn’t appear to come from the boiler or pump itself.