Control panel displays Sn2 and spa may not heat correctly or shuts down

Safety first: Shut off power at the GFCI breaker before working in the equipment bay.

• Reset power: Turn the breaker off for 2–3 minutes, then back on. If Sn2 returns immediately, continue troubleshooting.
• Locate high-limit sensor: In most Master Spas with Balboa or MS packs, the secondary sensor is mounted in the heater tube or on the heater manifold. Follow the labeled wires from the control pack (often SENSOR B or HI-LIMIT).
• Check connections: Unplug and replug the sensor connector at the control board. Inspect for corrosion, bent pins, or moisture. Dry the area if wet.
• Check sensor seating: Ensure the sensor is fully inserted into the heater tube or well and that the o-ring is intact. A partially inserted sensor can misread temperature.
• Test resistance: With power OFF and sensor unplugged, measure resistance with a multimeter and compare to a 10k NTC chart. If the reading is open, shorted, or far from expected, replace the sensor.
• Replace sensor: Install a compatible Master Spas high-limit/secondary temperature sensor. Lubricate the o-ring with silicone grease, insert fully, and tighten gently.
• Persistent Sn2: If a new sensor does not clear the code, the control board’s sensor circuit may be defective and the control pack may need replacement by a professional.