Hayward Thermostat or Control Relay Stuck Closed

Heater turns on even when thermostat is set low or off; water overheats.

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.

Possible Causes

Shorted temperature sensor, Stuck relay on control board, Miswired external control, Faulty thermostat circuitry

Safety First: Turn off power and gas immediately if the heater is overheating the water.

Verify setpoint: Confirm the thermostat is set below current water temperature and that the mode is not in Spa with a high setpoint.
Disconnect remote call: Temporarily disconnect external control wires to see if the heater stops firing.
Inspect control board: Look for signs of a welded relay or burnt components. Replace the board if found.
Replace sensor: If the water temperature reading is incorrect, replace the water temperature sensor.

Hard 4/5

Main Control Board

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