Control panel displays Sn1 and spa will not heat or may shut down

Safety first: Turn off power at the GFCI breaker and verify with a non-contact voltage tester before opening the equipment bay. Water and electricity are dangerous together.

Steps to troubleshoot Sn1:

• Power cycle the spa: Turn the GFCI breaker OFF for 2–3 minutes, then back ON. If Sn1 returns immediately, continue below.
• Access the control pack: Remove the equipment-side cabinet panel to expose the Strong Spas control pack (Balboa/Gecko style box).
• Inspect the sensor cable: Locate the primary temperature sensor plugged into the control board (often labeled TEMP or SENSOR A). Check for corrosion, moisture, or loose connection. Reseat the plug firmly.
• Check sensor routing: Ensure the sensor cable is not pinched, cut, or melted against the heater tube or pump motor. If insulation is damaged, the sensor should be replaced.
• Compare water temp vs. display: With power restored briefly, compare the displayed temperature to an accurate thermometer in the spa water. If the reading is wildly inaccurate or Sn1 persists, the sensor is likely bad.
• Replace the sensor: With power OFF, unscrew or pull the sensor probe from the heater manifold or sensor well. Install the new Strong Spas-compatible temperature sensor, ensuring the O-ring seats properly to prevent leaks. Route the cable away from hot or moving parts and plug it into the same port.
• Refill/bleed if needed: If you removed the sensor from a wet well, check for leaks after refilling and powering up.

When to call a technician: If a new sensor does not clear Sn1, the control board’s sensor circuit may be defective and the entire control pack may need professional diagnosis or replacement.