Boiler lockout

In live in a bungalow and have a potterton suprima he boiler.
I recently moved a radiator so drained the system and refilled once moved, but since then can't get the central heating to work. I've bled all the rads and the hot water works fine but after turning on the heating the boiler lockout light comes on after a minute or 2. The fault indicator shows overheat as being the problem.
Any ideas on what to do?

Have a look in your loft for auto/man air vent sounds like an air lock in the paperwork and getting no flow air in pump bleed via big screw in pumphead.

Cheers Mark

+1. Air.