neptune shower works intermitantly?

hi
i have a neptune solo shower 8.5 kw, it sometimes does not work, while testing to see if power was at the Solenoid Valve Assy it started, it sometime stops when in use and sometimes will not work when you turn it on and at other times it is fine, when it is not working the power indicator is not on although there is power in the unit, if i remove the power source to the Solenoid Valve Assy the led on the power in indicator goes of, can you tell me what fault the shower may have and if i can get parts
regards