Display shows Sn2 or SN2; spa may operate but with limited heating or safety lockout.

Safety: Turn off power at the breaker before working on sensors or the control pack.

• Reset and observe: Power cycle the spa. If Sn2 reappears quickly, the sensor or wiring is likely faulty.
• Locate secondary sensor: Identify the second thermistor on the heater tube or in a separate well. Confirm it is fully inserted and secured.
• Inspect wiring: Follow the sensor cable to the control pack. Check for nicks, crushed sections, or melted insulation. Reseat the connector on the board.
• Resistance check: With the sensor unplugged, measure resistance and compare to the primary sensor at the same water temperature. Large discrepancies indicate a bad sensor.
• Replace if needed: Install a new Hydropool-compatible high-limit sensor, ensuring proper insertion depth and secure mounting.
• Board fault: If both sensors test good but Sn2 persists, the sensor input on the control board may be defective and will require professional diagnosis.