Display shows SN1 or SENSOR1, spa may not heat or may shut down; temperature reading may be erratic or show dashes.

Safety first: Turn off power at the GFCI breaker before handling sensors or the control pack.

• Locate the sensor: Find the primary temperature sensor in the heater tube or sensor well. Trace its cable back to the control board.
• Inspect cable and plug: Look for cuts, abrasions, or rodent damage along the cable. Unplug the sensor from the board and check for corrosion or bent pins.
• Clean and reseat: If corrosion is present, gently clean the connector with electrical contact cleaner, allow to dry, and firmly reseat the plug.
• Test resistance: With the sensor unplugged, measure resistance across its leads with a multimeter. Compare to Arctic Spas thermistor specs for the current water temperature. A reading of near 0 ohms (short) or infinite (open) indicates a bad sensor.
• Replace sensor: If readings are out of range, install a new Arctic Spas-compatible temperature sensor, routing the cable away from high-voltage wires.
• If SN1 persists: A faulty control board sensor circuit is possible. Professional diagnosis of the control pack is recommended.