Constant air in central heating system

[Best]

Those manual vents are irrelevant and are only to remove air from those pipes on system fill up.
The thermostat operating fire pump is on wrong place, - should be on return at cylinder.
Whoever did the gas boiler is responsible for the air in system, but connecting into dual heating systems is a bit of a minefield and rarely are dual systems actually properly designed or piped.
I assume the cylinder has 2 coils?

 

[king of pipes]

Hard to tell from the pictures Geoff how the two systems are joined ? the vents and cold feed should be on the negative side of the pumps the pump on the boiler is on the return into the boiler where does the vent and cold feed connect probably a design error there somewhere. Cheers kop

 

[Baldy Geoff]

Those manual vents are irrelevant and are only to remove air from those pipes on system fill up.
The thermostat operating fire pump is on wrong place, - should be on return at cylinder.
Whoever did the gas boiler is responsible for the air in system, but connecting into dual heating systems is a bit of a minefield and rarely are dual systems actually properly designed or piped.
I assume the cylinder has 2 coils?

 

[Baldy Geoff]

Not sure about the coils to be honest. What I have recently noticed is that the thermostat connected to the downstairs stove when turned off and on seems to turn the gas burner off and on as well. Don't think this is right.