How do I fix my Triton Opal shower?

My Triton Opal shower (c2005) has a permanent fault:
when you switch ON the mains 'pull-cord' it immediately starts up running cold water through the shower head. The LED's display power and heat II then after a brief moment other LED's illuminate.

If anyone can help with this and/or provide me with a circuit diagram of the two PCB's?

Many Thanks