Bosch Worcester 28i RSF Combi Boiler?

You help would be very much appreciated........I have noticed water dripping on to the floor underneath my boiler and it is tripping the board.

I have taken the front cover off and the silver cover which covers the main components of the boiler. After looking at the very old instruction manual, I can see water dripping out of the 'automatic air vent' which is dripping down onto exposed wires and causing the electrics to trip at the board. It looks like the automatic air vent is missing a screw to stop it from leaking because I can see the thread inside of the hole where the water is leaking from.

Could you please tell me if i am right and if i bought a screw for it, does it have to be tightened or partially tightend with it being automatic air vent?

Many thanks

James
April 2011