Heat Siphon will not shut off

After running ok for a period of time and turning on when heat is required and off when the set point is reached, you now have an overheated pool or spa and the unit just keeps running. Alomost always this is due to one of two problems

  • Contactor is welded shut after experiencing excessive chatter, a lightening strike or prolonged low voltage power
  • Thermostat bulb or water temperature sensor is out of the heat exchanger well and is sensing the outside air temperature instead

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