hi there i need some info on filling my boiler, its a bosch worcester 24 cdi rsf , problem is i cant seem to fill the system back up to its normal pressure of just under 1 bar it has a built in filling loop under the boiler i have to insert a white filling key in to the loop then turn a little grey knob to fill ihear the water for a second untill it gets to the key bypass but then stops and no water enters the system at all do i need to bleed the radiators before it will fill ? or do i have a faulty valve? any ideas would be great, thanks!