glowworm c30i F5 fault?

hi there, ive just tried to fire up the boiler in a house i bought, its been off for 6 months at least. system was drained, so ive filled it up to 1 bar, switched the boiler on and it fired up ok, according to the temp gauge it was heating up quickly then it stopped, switched control back to 0 waited 5 secs and switched back to 1, nothing, after a few attempts i switched off the fuse spur and tried again, still nothing, the bolier is reading F5, can anyone help please? thanks in anticipation geoff