I have recently had a central heating system installed a Ravenheat Combination Boiler with Timer. Natural Gas. Model RSF84E(T) there are 7 rads on the system if all rads are on and I only have two rads upstairs the ones upstairs start to bang and vibrate heavily the only way to stop this is to switch off the rads as soon as I do this the noise stops can anyone explain what is going on. HELP!!!!