Control panel displays Sn1 and spa will not heat or shows dashes for temperature

Safety first: Turn off power at the spa’s GFCI breaker and verify with a non-contact voltage tester before opening any panels.

This code usually indicates the main water temperature sensor (thermistor) on the heater manifold has failed or is not being read correctly.

• Power reset: Turn off the GFCI breaker for 2–3 minutes, then turn it back on. If Sn1 returns after a few minutes, continue below.
• Access equipment bay: Remove the front cabinet panel to expose the control pack and heater tube.
• Locate the sensor: Find the primary temperature sensor threaded or inserted into the heater manifold, with a cable going to the control board labeled TEMP or SENSOR.
• Check connections: Unplug the sensor connector from the control board, inspect for corrosion or moisture, dry if needed, and firmly reconnect.
• Inspect cable: Follow the sensor cable for cuts, pinch points, or rodent damage. If damaged, the sensor must be replaced.
• Compare water temp: With power restored, compare the displayed temperature to an accurate thermometer in the spa water. If the reading is wildly inaccurate or Sn1 persists, the sensor is defective.
• Replace sensor: With power OFF and water level below the sensor port (or with isolation valves closed if equipped), unscrew or pull the old sensor from the heater manifold, install the new Artesian-compatible thermistor with a new O-ring, tighten snugly (do not overtighten), reconnect to the board, then restore power and test.

If the new sensor does not clear Sn1, the control board’s sensor circuit may be faulty and should be evaluated by a qualified spa technician.