I have a standard gas boiler with 2 circuits, 1 running central heating and 1 running to the hot water cylinder. My question relates to the pressure of the system. I can charge the system using the filling loop to over 1 bar and during the course of the heating cycle this increases. A couple of days later the pressure has dropped right down and if I recharge it it falls again. I have recently moved house and my old combi boiler did not behave like this. Is this normal for this type of boiler or do I have a problem somewhere?