AquaCal Thermostat Overshoot / Control Hysteresis Issue

Water temperature overshoots the setpoint by several degrees before the heater shuts off.

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Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

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Possible Causes

Water sensor installed in poor location with delayed response, Control board hysteresis set too wide, Sticking relay keeping compressor on, Sensor out of calibration

How to Fix / Troubleshooting

Safety first: Turn off power before moving sensors or accessing the control board.

  • Verify sensor location: Ensure the water temperature sensor is installed where it senses mixed pool water, not directly at the heater outlet.
  • Compare temperatures: Use a pool thermometer to compare actual water temperature to the display. Replace the sensor if readings are inaccurate.
  • Control settings: Some AquaCal models allow adjustment of differential/hysteresis only by technicians. If overshoot is large, consult AquaCal support.
  • Relay check: If the compressor continues running after the control indicates OFF, the compressor relay/contactor may be sticking and should be replaced.
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Repair Difficulty

Medium 3/5

Required Part

Water Temperature Sensor
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