Reservoirdog

I have a Pentair Master Temp pool heater that shut down one day. I removed the thrermistor and it was corroded. I replaced it and fired it up and the heater worked for about two minutes and then the red light service heater came on and the heater shutdown but the fan still ran. After about 45 seconds the red light would go off and the heater would turn back on and heat. This cycle continues. I pulled the circuit panel off and the HLS comes on along with the red service heater light. I replaced the HLS HGS sensors. The problem continued so I replaced the thermal regulator and bypass valve. I tested the regulator too. I replaced the HLS sensor a second time just incase the one I bought was bad. I took a jumper and jumped the wires for the HLS sensor and the heater works great no problems. But I have tried two new sensors and both make the heater cycle. Do I have a bad board? I am out of things to replace.