I have water leaking from the automatic air vent of my combi boiler (sime super 90)which stops when I tighten the small black cap. Should the cap be loose? or is this a faulty vent? Or is something else causing it to leak?

Terry Evans, May 2008

how to get air pressure out of boiler

anthony, September 2011

The cap should be loose to allow air to automatically vent out, the cover just stops dirt etc from getting in.
The automatic air vent should never let water out, it is clapped out and should be replaced......... they only cost a few quid.

John ( Wirral ), August 2008

yes the cap should be loose to allow it to automatically vent any air, it valve is most likely clogged with sluge or scaled causing it to either stick or not seat correctly

close that cap and allow the boiler to run, it should be ok, but if you start getting unexplanined boiler lockouts all the time it may need to be replaced (then again, shouldnt be big pockets of air in your system if its correct)

T, May 2008