the boiler drops pressure when the hot water is used ?

So does the pressure drop or not, make your mind up. Should not be a t 3 bar. Most boilers are fitted with an over pressure valve, which is rated at 3 bar. Probably should be about 1 bar when cold. Noise could be the over pressure release opening, which it would as by calling for heat, the boiler pressure would increase past valve setting. Drop your pressure to 1 bar when cold, radiators every thing cold. When IF you post again, try putting make and model and making up your mind if the pressure drops or not.

SD
December 2012