Hi can anybody help with a problem i'm having my boiler is a old valiant which has just got a strange fault. the boiler heats water no problem the heating however fires up warms downstairs radiators and the bathroom 1 the others barely get a glimse of heat they are all bled i've noticed that the pressure gauge climbs upto 2.5 bar during heat up then the boiler shuts off the pressure drops a little the boiler starts but then shuts off again and again anybody any ideas or had this problem