Hi Chris
Ours did the same thing a few months after we got it so was under warranty. The repair guy said it was caused by loose connections on the circuit board, apparently re-soldered something and it was fine.
Thing was, it developed the same fault about three weeks later and we called them out again.
It was the same guy who came out and replaced the main circuit board inside the shower. He then admitted it was fairly common fault with this model and he had been out to quite a few of them.
Ours is now about three years old and has started to play up again - low pressure light comes on and it switches to cold only.
Simon, September 2008