Help Air in system

[Als01]

Please can any one help, I keep getting air in both my heating & hot water system although the heating is now off for the summer.I can bleed the heating via the upper rad where the air gathers but cant understand why this keeps happening. I have inspected the system & pipes & there are no leakes.
There is an auto vent fitted to the hot water side by the 3-way valve (Braukman) but this seems to make no difference,this is just before the hot water cylinder. You can hear the pump churn as the air passes by. Any ideas please would be greatly appreciated.

 

[gas4you]

Check you have water in the F & E tank in the loft first. (assuming you have one)

 

[Als01]

Just checked, yes there is water in the expansion & makeup.
Its part of the hot water cylinder the top of the cylinder is split, does this make sense !!

 

[gas4you]

From your description I think you are referring to a fortic or combi cylinder.

The small tank on top of this would be feeding the HW cylinder, not the CH.

The CH F&E tank is usually seperate.

I assume you do not have a loft? If you do have one check there for the F&E tank.