The above is quoted from your first post !!"There are no radiators being fed by the boiler so it seems simple but I can't see where to air bleed this pump ".
I took the nut off where you bleed it to get a better flow.Is the F&E tank full of water ? Are all rads full of water ?
You may have a blocked feed ,and system full of air.
Did you bleed the rad or drain it ,as you told us earlier.
Just one thing.I just had a look at that screw that I was told by ianmcd not to touch and that it needed to be aligned with the pipe (if I got that right)Thats great , hopefully your sorted .