Depressurises over night but when recharged with cold water to 0.5 bar fuctions again oK. Is this the Pressure Vessel. The boiler is in my house and is 12 years old.
PS I'm an ex Transco Service engineer

mal, December 2008

is the pressure relief valve dripping outside when heating is on or off. if it drips when heating is on and the pressure gauge gets up to 3 bar the vessel either wants repressurising or swapping. if it wants a new one its cheaper to fit an external one somewhere close to the boiler on the flow. try that.

stuart priestley, December 2008