worcester bosch combi boiler loosing pressure

[proelitegas]

just had a call from a customer..when boiler stat reaches temp burner turns off and pressure on gauge drops and noticed it discharging from the relief valve...going to look at it tom im thinking checking pressure in expansion vessel,checking the pressure relief valve...it could also be a clogged up plate exchanger...any advice would be appreciated

 

[bob the plumber]

your probably right on the first one, expansion vessel is duff. You will have fun replacing that unless you decide to stick a new expansion somewhere else on the system