SHUT OFF THE FEED & RETURN PIPES UNDER THE BOILER & DRAIN VIA THE SAFETY VALVE. (SPRING LOADED KNOB WITH RED TOP) UNSCREW THE AUTO AIR VENT & SCREW IN A NEW ONE. OPEN FEED & RETURN PIPES & REFILL & PRESSURISE TO APPROX 1 BAR. ITS THAT SIMPLE.
DAVE12
April 2007