Air in system - bad design?

[Bunker]

Im mainly a oil boiler service engineer but do get involved in systems sometimes. I was asked to look at a system which is constantly full of air, always bleeding some of the rads. In the loft I found the expansion pipe to be gurgling and Im sure it was blowing and sucking.
Looking at the design (see below) there are a few concerns, but its not really my thing:

Im concerned that the pump will be dragging air in from the expansion pipe.
Im concerned that the hot water primary return is only 15mm
Will air be getting in at the pump valve leaks?

Btw, missing from the photo is a manual air vent in the HW flow.

Its a small 3 bed house.

Any comments would be welcome

Thanks

 

[Mike Jackson]

Needs converting to a close couple feed and vent arrangement. It will keep dragging air down the vent with that configuration.

 

[mfgs]

As Mike said, the vent and feed need repiping to cure it.

 

[josh]

Agree. Have been to a job where gravity primaries have been made pumpd but they hadn't alterd the cold feed and vent, was pumping over like a gooden.

 

[Bunker]

I 'fixed' this job back in feb by combining the F&V up in the loft (on the 22mm), I also fixed the leaky pump valves, but have just heard from the managing agent that the tenant still needs to bleed the bathroom radiator once a week. All other rads are fine now. When I first went there, I put a match to the air in the bathroom rad (not towel rail) and it didnt ignite so assumed it was air. Is it worth sticking one of those auto bleed rad valves in? Not sure what else to try.