Display shows 'SNS' and heater will not fire; temperature reading may be erratic or blank.

Safety first: Turn off electrical power to the heater and close the gas valve before servicing. Allow the heater to cool.

Steps to address SNS error:

• Power cycle: Turn power OFF for 30 seconds, then ON. If SNS returns immediately, proceed with sensor checks.
• Locate the water temperature sensor: On most Raypak digital pool heaters, the sensor is threaded into the inlet/outlet header or mounted in a sensor well on the water manifold with two small wires leading to the control board.
• Inspect wiring: Follow the sensor wires to the control board. Check for cuts, rodent damage, or melted insulation. Reseat the connector on the board.
• Check sensor resistance: With power OFF, disconnect the sensor from the board and measure resistance with a multimeter. Compare to Raypak’s temperature/resistance chart (e.g., around 10kΩ at 77°F for many NTC sensors). A reading of 0Ω (short) or infinite (open) indicates a bad sensor.
• Replace the sensor if defective: Drain water from the heater header if necessary. Unscrew the old sensor, apply appropriate thread sealant to the new Raypak sensor, and install. Reconnect wiring and restore water flow.
• If sensor tests good: The issue may be on the control board sensor circuit. Inspect the board for corrosion or burn marks; replacement of the temperature control board may be required.

Note: Always use a Raypak‑specified temperature sensor to ensure correct calibration.