Water keeps flowing after power-off on Triton t300si?

Hello,

My Triton T300si has recently developed a fault whereby when I turn off the power on the control unit the hot water stops but instead of the water flow stopping it keeps flowing at the same pressure but it is now cold. Triton have been cryptic about the actual possible cause but have alluded to the notion that it might be the PCB...they wouldn't tell me which one (remote pack or main unit) and would also not tell me how to test to check.

At the moment to stop the water flow I have to turn the shower off at the main board.

Any ideas/help would be very much appreciated!!