Hi Kenneth, What is the make and model of your boiler? It could be that you have a leak on the c/h system or the expansion vessel need's recharging with air. The vessel should be checked at every service. Check the exhaust pipe from the boiler safety valve which should be outside, if it dribbles water when the boiler is on then it is nearly certain the vessel has lost it's pressure. Is the pressure gauge reading higher than normal?
menditman., January 2010