Cheers. In work now so will try again when I get home late afternoon.Opening the vent screws and getting rid of any air in the rads. (Bleeding the rads)
Not sure about the one with the red handwheel (you would have to trace it but let it be just now whatever its opening is).
The two brass valves, immediately above and below the pump MUST be fully open, get a adjustable spanner or even a pliers and try shutting first, if they are open then you should get 3 to 4 turns to shut, then immediately reopen, ie they must be ~ 3 to 4 full turns open from fully shut.