Control panel displays Sn1, SN1, or SENSOR 1, spa may not heat and may shut down.

Safety first: Turn off power at the GFCI breaker before opening the equipment compartment.

• Locate temperature sensor: On Aquaterra Spas using Balboa-style packs, the water temperature sensor is typically threaded into the heater tube or inserted into a thermowell near the heater.
• Inspect wiring: Check that the sensor plug is firmly seated on the control board and that the cable is not pinched or damaged.
• Check for corrosion: Look for corrosion on the sensor connector pins. Light corrosion can sometimes be cleaned with electrical contact cleaner and a soft brush.
• Reset power: Restore power and see if the Sn1 code clears. If it returns immediately, the sensor is likely defective.
• Replace sensor if needed: With power OFF, unscrew or pull the sensor from the heater tube/thermowell, install a compatible Aquaterra/ Balboa temperature sensor with new O-ring or sealant as required, and reconnect to the board.

If replacing the sensor does not clear the error, the control board sensor circuit may be faulty and will require professional diagnosis.