why are you only meant to bleed radiators with the central heating turned off?
Had a problem recently with 2 rads not getting hot with an air lock , tried everything , in the end i lock all rads off except the 2 that wernt getting hot , turned heating on and bled the 2 troublesome rads with the heating on, ( my thinking was that i would give the 2 air locked rads the full force of the pump ) ... sorted the problem , so that's why i asked the question
cheers
ste