The problem is with the thickest cable inside, that carries the power into the shower. I've had the same problem and i fixed it by cleaning up the cable and re-fitting it. Its now two months later and its failed again.
Thing is, i cant find a replacement cable and i cant remember what the actual gage of cable it is since i replaces the sheathing on it.
If i could find where to get the cable i'd be fine. Local B&Q doesnt have it.
Tam Denholm
July 2008