I have an Abbey 495 Vogue and this week-end we were away when I too had the problem with air in the water system. I changed the O rings on the inlet, re-pressurised the accumulater to 20 psi.
Still it was doing it, there was a clear filter housing before the pump, checked that, still no improvement.
WEnt to my local dealer near Thame, seems the black housing which the clear filter bowl screws onto may have cracked allowing air in. No water was leaking out at ll over the week-end {pipe delimiter}I must add.
Took out the housing last night, only to find a hairline crack in the housing.
This will be replaced and cure the problem. Check out the housing first.
Thanks to the dealer much appreciated.
HTH