Leak from boiler........ any ideas?

[Dr Wu]

Hi there We have a 4 year old potterton profile wall mounted gas combi boiler, one of these: http://www.potterton.co.uk/products/literature /Potterton_Profile_40eL-80eL_User_Guide.pdf We've noticed recently that there is an occassional slight leak (usually when the boiler is off) of water which seems to be coming from the cap at the top of the return flow pipe. (there's 2 pipes on top of the boiler, this is the one on the right which runs up from the floor not the one which comes down through the roof from the water tank) There's a metal screw on top of the cap which I did tighten and that seemed to stop the leak for a while but now it's back. Any idea what the problem might be? Thanks

(ps: the boiler works perfectly well)

[Dave G]

Hi That thing you screwed shut should be open it is an automatic air vent (AAV) if it leaking from that, it will have to be changed
turn off at mains and drain down
exchange for a new one from potterton
No major problem and if calling a plumber he shouldnt charge a fortune
I SUGGEST A PLUMBER REGISTERED WITH THE INSTITUTE OF PLUMBING.good luck

[Dr Wu]

Thanks Dave.