alpha cb24/28?

Hi, Have the same problem as MEL JOHN (APRIL 2011).
CH ok and DHW but when DHW ON ONLY-NO HOT WATER. I read on the net it may be a sticky valve in the DHW valve (switch). Cleaned valve then following instrucs started to fill boiler, presure gauge raised to green. Turned presure release valve as suggested in the strucs one click, gush of water/air. Now boiler will not fill,no water running through loop. any suggestions.