Why are my radiators are not heating?

Hi I have a Glow Worm 2 18 sxi Boiler which is filled via a Glow Worm Fluropro tank. I turned my radiators on for the first time since April on Monday and they are yet to heat. The pressure on the boiler and the tank is both 0.6, which I think is too low and may be causing the problem, however, this is an assumption. I have bled the radiators and all are fine.... Any help would be greatly appreciated!