pressure is set at 1 bar when cold filling loop valve is closed and filling key is removed but when central heating is run pressure goes up to 3 1/2 bar and water comes out of release valve overflow pipe.When central heating pressure is reduced again back down to 1bar and run again pressure rises again the same.

mr Parry, October 2007

hot water is ok but no heating

steve, October 2011

Get a replacement expansion vessell the diaphragm is perforated provided that the check valve on the internal filling loop isn't passing water.

shaz the gas fitter, October 2007

It sounds like your expansion vessel has gone, they are a bit of a pig to replace with original part. If you have room you can fit a remote expansion vessel onto the return pipework, a 12lt vessel should cost no more than forty pounds.

colin, October 2007

if pressure rises(over a couple of hours) with no heating then the plate heat exchanger is passing. if pressure rises fairly quickly with heating then drain system, press shreider valve in red expansion vessel, if water comes out then vessel gone, if nothing then use a car foot pump and pressurise to just under 1bar refill system and happy days

waynethegas, October 2007