Water slowly leaking out of overflow pipe when 3bar is reached then needing to be refilled every three to four hours. Can fill up at bedtime then in morning have to top up again even though the heating has been turned down low and doesnot come on all night

P Trunkwald, May 2009

if your system pressure is rising when heating is on it is likely you have a prob with the expansion vessel. if the pressure rises from "0" to 3 bar when heating etc is off then your boiler is leaking through the heat exchanger. Either the plate or gas to water depending on which boiler you own.
best of luck

boilerdoktor, May 2009

re-pressurize expantion vessel

b, May 2009