I have a Pentair Mastertemp 400 pool heater that was installed about 2 years ago and has been working great up until recently.
This issue is that the 'Off' button is not working. When the button is pressed nothing happens. Some quick research leads me to believe this is possible a bad membrane.
The other issue is the pool heater does not turn on automatically when the pool timer/pump kicks on. The unit turn on, but I have to hit Pool heat button to manually turn the heater on.