There is a known fault with this shower. Do a search. Basically there is a control board inside the shower with a switch at the bottom. This switch is pressed by a piece of plastic that hits it when there is sufficient pressure. The switch stops working and Triton get to charge you for an...
Cheers. Cheapest I found was one from Ideal Standard for £189 complete. They also did two others. Decided to replace soil stack in the end, but thanks for the replies.