Can any one help? My Potterton 80 combi boiler, the bar gauge indicates red high pressure when the central heating is running and the radiators are hot with water coming out of the overflow. When the system reaches room temprature the boiler turns off leaving the pump running but the bar gauge falls slowly to below bar 0 into the red on the dial. I puts some more water in the system to bring the gauge back to bar 1.5 but on heating up the cycle repeats. I have spoken to Pottertons help line and have been told that the red expansion tank on the top of the boiler may be blocked up causing the extra pressure to build up, but they wanted to speack to the engineer before telling me anything else.