Triton Rapide 4 Shower, Repair to circuit board?

I need to repair a Triton Raide 4 shower. Have had to replace it with a new one but wish to repair the old one as a spare. Problem is on circuit board (main). Normal operation of all features until turn off when heater shuts off but water solenoid is not released meaning water still flows from shower. This is rectified by removing mains from unit when solenoid drops out and flow stops. Triton were out of stock of board when replacement needed hence purchase of new Rapide 4+ was necessary. Probably due to pitted contacts on one of the relays or failure of thyristor or supply component to solenoid. Possibly due to failure of circuit sensing reduction of temperature in heater as the unit normally runs on for a short period after turn off. NEED CIRCUIT DIAGRAM to assess problem and try repair.