Pentair minimax plus 400 won't turn off

[Nwebster]

Hi, I have a pentair minimax plus 400 that heats both a pool and a spa. The problem is the heater does not turn off when spa or pool get to set temperature. Heater has to be turned off manually. I replaced the thermal sensor, the two hi limit switches and the thermal fuse. All seemed to be ok but I swapped them out anyway. Still will not turn off at temperature. My next guess is the thermostat board or the two potentiometers. The fact that both pool and spa are affected suggests that it's not the pots. Anyone have any suggestions before I buy a new board?

Thanks.

 

[azazel]

Is the water in pool and spa at the same temperature? If the pool water is lower then the spa water the heater is going to keep running till the pool water hits the cut off temperature. And with a pool being tied into the same heater as spa I would think it would cause the heater to run cause if pools outside it with no cover its constantly losing heat. Which would cause heater to keep running.

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