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

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

• Step 1 – Power cycle: Turn off the GFCI for 5 minutes and restore power. If Sn1 returns immediately, the sensor circuit is likely faulty.
• Step 2 – Inspect sensor wiring: Locate the temperature sensor threaded into the heater tube on the Catalina control pack. Follow its cable to the control board. Check for cuts, rodent damage, or pinched sections. Ensure the plug is fully seated and corrosion-free.
• Step 3 – Compare temperature: If the spa is running, compare displayed temperature to an external thermometer. If the reading is wildly inaccurate or Sn1 appears intermittently, the sensor is suspect.
• Step 4 – Replace sensor: With power off and water level below the sensor port (or with valves closed), unscrew the old sensor from the heater tube. Install the new Catalina-compatible temperature sensor with a new o-ring, tightening snugly but not over-tight. Reconnect to the board.
• Step 5 – Test: Restore power and monitor for 15–30 minutes to confirm the error does not return and temperature readings are stable.