Air in hot water

[willjm]

For several weeks I've had intermittent air coming out of my hot water taps. It is most noticeable downstairs. I have a solid fuel boiler and a vented system with hot water cylinder upstairs and cold water cistern in the loft. This has coincided with my 33 year old boiler overheating and tripping out; don't know whether the two are related. I don't hear water boiling. I don't understand where the air is coming from. Does anyone have any ideas?
Central heating is working as normal.

 

[JohnD]

if you bleed the highest radiator in the house, does water squirt out vigourously?

when you look at the tank in the loft, is the water at its normal level?

 

[willjm]

Yes, I've checked all the radiators and the water in the tank in the loft is at the normal level.