Air lock oin my System mate 2000

im struggling to get my system up and running again after drain down to fit new isolating valves either side of lhs pumps..
I have an air lock that wont budge!!
The rhs pump constantly running and very hot, if i undo the bleed screw on front it just sucks in more air..
Wont fire boiler which i recon is due to the air lock?

Bleed pump when NOT running.
Mike

Replaced pump seems to bleed ok now although keep getting f5 error on my boiler which is overheat.
Boiler ran all night ok then went to f5 again. Any ideas

All pumps seem to be working and I've bled the system to death!!

Also can't get the systemate to call for boiler to fire unless I put the Switch Live connection from boiler into Live feed on Pcb? Is this a sensor problem or requires new board?