Heater displays SNS; temperature readings are erratic or incorrect.

Safety First: Turn off power before working on low-voltage sensor wiring.

• Inspect sensor location: Locate the water temperature sensor on the inlet/outlet header. Ensure it is fully seated in its well.
• Check wiring: Follow the sensor wires back to the control board, looking for cuts, abrasions, or loose plugs.
• Clean connectors: Disconnect and reconnect the sensor plug to wipe oxidation from the contacts.
• Replace sensor: If SNS persists, replace the water temperature sensor with a Hayward OEM thermistor.