problem with my SIME friendly 8088905?

My SIME will heat the radiators as normal , but it won't do any hot water . The pilot light is always on , and when the rads are on the flame kicks on and off intermittently to heat the rads , but when you turn on the hot water taps , the flame doesn't kick into life , it just stays on pilot ???
Also where can I possibly get a manual downloaded from possibly ? :-)

Regards JT