The pressure on my boiler keeps dropping to ½ or below and when the heating is on it goes up to 4. Sometimes the fault light comes on when the pressure is low and I try to switch the heating on or try to use the hot water tap. I have to top up the boiler most days and even then sometimes the fault light comes on. I paid an engineer £60 to fix it but he only replaced the air pressure switch which has not made any difference at all. Apart from topping up the expansion vessel has anyone got any suggestions?

RHP485, December 2010