Worcester 28si slow flashing red light - no heat or hot water?

a week ago i bled the radiators, topped up the boiler and tonight when i tried to run a shower there is no hot water - i checked the front of the boiler and have a red slow flashing light on the central heating indicator. I have pressed the reset button and the boiler tries to fire up but to no avail. Any ideas how I can fix this at all would be very gratefully recieved. Many thanks