I have a Gainsborough 400X shower bought around 1998, it works fine for about 2-3 minutes then the water just stops, you hear a clunk from the water pipes as it shuts off - just as if you had turned it off normally. The power light remains on but the High / Low power light turns off. The shower will then not work again for 10 minutes or so, after this time it will work for another 2-3 minutes again, and so on...
Sounds like the solenoid is shutting the water off but why? is the solenoid faulty or is something else causing it to shut off the water? The water is not getting any hotter than normal and pressure is OK.
Regards
Julian