No hot water from Danesmoor bolier?

I have a boiler danesmoor 15/90 and now can not get hot water from taps. ..just cold running water. Have checked thermostate in cylinder and replace as had spare.
Would it me a 3 motorised valved or the 2 way motorised valve or the relay?
Once the boiler is turned on ,it shortly afterwards shuts down with the hot water switch on but if you turn off the hot water the boiler stays on for heating and works fine.Sounds like electical