as per title.
Having suffered a leaking (and then some !) AAV after flushing and inhibiting my Vaillant boiler ...
I removed the offending AAV, dismantled, cleaned, refitted, and it no longer leaks. Two days running, and no air in system (and pressure is being maintained, so the expansion vessel seems to have done the trick).
However, the original cap had deteriorated and the top cracked off.
Googling doesn't seem to help. I know Grundfos/Vaillant would *like* to sell a new pump for the want of a cap, but I can't believe they aren't available as a separate item ?