Hi there hope someone can shed some light on a noise problem from my upstairs neighbours heating.she has a potterton puma 8yrs old, trv's on radiators.the pump broke down was replaced,now when her heating is on a loud noise like a tap running occurs through out her system,gets louder the longer its on also makes a howling noise sometimes as well,goes away for 10 to 20 seconds when she turns her hot water on then starts up again sometimes louder.She has had the pump changed to no avail.the noise is continual,droning like the main tap is on full,has never been like this before,only after the pump broke down any help would be much appreciated.Two different plumbers have been stumped.