I had a Main Combi 24HE boiler installed in January when my old Ferroli finally gave up the ghost. As far as I can remember the system was not particularly noisy when using it up until the spring, but since I have had it back on this month there is quite a loud humming noise coming from the pipes and rads. It's kind of cross between humming and a water rushing type noise. There are only 4 rads on the system (living room, kitchen and 2 bedrooms) and it's probably loudest in the living room. The boiler isn't particularly loud. I've read that reducing the pump speed can help but there doesn't seem to be any means for adjustment on the pump (although the instruction manual says that there should be). Any help or advice would be very much appreciated.