When boiler cooles down the pressure drops all the way down, boiler wont start, once the water pressure is topped up, and the boiler starts as the temperature rises the pressurt goes through the roof?

Alex, January 2012

Alex .this is typical of a pressure / expansion vessel fault (The orange thingy) it will have a valve on it like a car tyre, it will have little or no air pressure in it, causing the system pressure to rise rapidly when system is on, which then vents through pressure relief valve losing water from the system. System cools down and the water contracts = loss of pressure. I take it that apart from low pressure everthing else appears to work ok ? A relative simple fix normally with a car tyre pump or bike pump with a gauge. Off line now whilst 1900hrs

Colin West Yorkshire, January 2012