I have had this happen twice in about 8 years.
The first time, 4 years ago, I ordered a new power PCB, swapped it over and it started working again.
The second time, very recently, I tracked it down to a transistor on the control PCB, which is the PCB attached to the front of the shower behind the buttons. It's the top-most transistor, a 2N5551, and it was open circuit. There was also a resistor on the board, which had clearly been too hot ... brown PCB around it. I swapped the transistor and the shower is working again.
The symptoms looked the same to me, but were due to different underlying failures.
So I think it's worth checking for the hot resistor on the control PCB before replacing the other one.
will, November 2010
