Removing Air from Sealed System

[btgriff]

I've had a couple of radiators off for decorating and now I'm suffering with (what I think is) air trapped in the system. I isolated the radiators closing the valves either side, did my decorating, then put them back. I bled the air out and topped up the pressure.
Now when I switch the central heating on from cold everything works fine. All the radiators get hot and work fine. However after about 90 minutes I start hear something 'bubbling' through the radiators at the TRVs. To me it sounds like trapped air.
Is this dissolved air being released as the water is heated? How do I get rid of it. When I bleed the radiators I get water out. I know the boiler has an auto vent but how do these work, are they any good.
Its a sealed system using Ferroli Modena 80 E combi boiler with all radiators having TRVs except the bathroom one.

Any advice. Thanks.
Ben

 

[gigz]

Could be the valves (trv or lockshield) are'nt open properly. Have you got inhibitor in ? If yes bleed all rads again after a couple of days (boiler off downstairs first) should be ok. Auto air vent wont get the air out if its lower than the rads.

 

[btgriff]

I'm not sure about inhibitor, depends on the previous occupants. On the list of jobs here was to flush it then refill with inhibitor.
btw, the boiler is in the airing cupboard and is the highest point in the system.
Whats odd is I hear the noise go round to different rads. Air is supposed to collect in radiators, yes? It doesn't move round the system with the water.

 

[gigz]

There is an auto air vent in the boiler, read the instructions it could be closed (close it then open 1 full turn) Reading your post again it could be the trv head, when you hear it again very slightly adjust the trv in question.