I have a 2003 Hot Spring Tiger River Bengal which won't heat. I replaced both thermistors but if I have the main (4 pin) thermistor lead connected to the main board it trips the system (not the power feed ground leakage) and flashes the red light on control panel. If I disconnect this sensor then main pump and lights work fine, the temperature display works and the (green) ready light on the control board is lit. No heat to pool and ozone system seems to be inoperative. Any clues, please ? I'm about to test heater voltage when rain stops (!) What should I expect to see, please ?