Display shows Sn1 or SN1 and the spa may not heat or may shut down.

Safety: Disconnect power at the GFCI before accessing the control pack or heater area.

• Power reset: Turn the spa OFF at the breaker for 2–3 minutes, then back ON to see if Sn1 clears. If it returns, proceed with inspection.
• Locate the sensor: Find the primary temperature sensor inserted into the heater tube or mounted in a sensor well. Follow its cable to the control pack.
• Check connections: Unplug the sensor from the control board and inspect for corrosion or moisture. Dry the connector if needed and reseat firmly.
• Visual inspection: Look for cuts, abrasions, or rodent damage along the sensor cable. If damaged, the sensor must be replaced.
• Resistance test (advanced): With the sensor disconnected and water at a known temperature (e.g., ~25°C / 77°F), measure resistance across the sensor leads. Typical spa thermistors read around 10k ohms at 25°C. A reading of open (infinite) or short (near 0) indicates a bad sensor.
• Replace sensor: If faulty, replace with a compatible Hydropool temperature sensor, routing the cable away from high-voltage wires and securing it to prevent chafing.