sime super 90

[kaseyfour]

hi can any one help i've got a sime super 90 that keeps building the pressure up to over three bar and then dumps it out through prv valve. i have changed the ball valves both sides of the filling loop, the other thing i think it might be is the heat exchanger . anybody got any idea please

[gucciman]

if the pressure is rising while the heating is on then its a problem with the expansion vessel, it either needs re-pressurising or possibly replacing it it has failed completely.

if the pressure is rising overnight when the boiler is not running then it is a prob with the heat exhanger, either the main exchanger or the secondary hot water exchanger depending on what system your boiler uses.