Could be a few things;first is the filling loop definately shutting off?remove one end of hose if external loop to check.Does the pressure only rise when heating is on;if so it is probably an expansion vessel fault; either it needs recharging to 1 bar pressure or the pipe to vessel is blocked or the expansion vessel is gone.
Mike
January 2010
howtomendit.com for free repair help, information and advice.
