Display shows Sn1 or SENS1; spa may not heat or may shut down.

Safety first: Turn off power at the GFCI breaker before touching any wiring or sensors.

• Step 1 – Power reset: Turn off power for 5 minutes and restore. If Sn1 returns immediately, the sensor or wiring is likely faulty.
• Step 2 – Locate sensor: On Nordic tubs using Balboa-style packs, the water temperature sensor is threaded or clamped to the heater tube. Identify the sensor labeled TEMP or SENSOR 1.
• Step 3 – Inspect wiring: Check the sensor cable for cuts, abrasions, or rodent damage. Ensure the connector is fully seated on the control board and free of corrosion.
• Step 4 – Compare temperature: If the spa will run, compare the displayed temperature to an external thermometer. If the reading is wildly inaccurate (e.g., 32°F or 140°F in normal water), the sensor is bad.
• Step 5 – Replace sensor: With power off, unscrew or unclamp the sensor from the heater tube. Be prepared for a small amount of water. Install the new Nordic-compatible temperature sensor with proper sealing (O-ring or Teflon tape as required).
• Step 6 – Test operation: Restore power and verify that Sn1 is cleared and the temperature reading is stable.