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 any panels.

• Power cycle the spa: Turn the GFCI off for 2–3 minutes, then back on. If Sn1 returns immediately, continue below.
• Access the spa pack: Remove the equipment-side cabinet panel to expose the control pack (Canadian Spa Company control box).
• Inspect the sensor cable: Locate the primary temperature sensor plugged into the spa pack (usually labeled TEMP or SENSOR 1). Check for cuts, rodent damage, or pinched cable along the shell.
• Check the sensor plug: Unplug the sensor from the control board, inspect pins for corrosion or moisture. Dry gently and reconnect firmly.
• Test the sensor (if you have a multimeter): With power still OFF, disconnect the sensor and measure resistance across the two sensor leads. Compare to a 10k or 20k thermistor chart (typical spa sensors are ~10kΩ at 25°C/77°F). If reading is open, shorted, or far off expected value, the sensor is bad.
• Replace the sensor: If faulty, unscrew or pull the sensor from its well in the heater tube or shell, install a new Canadian Spa Company-compatible temperature sensor with fresh O-ring, and tighten snugly (do not overtighten). Reconnect to the same port on the spa pack.
• Restore power and test: Turn GFCI back on, clear any error by power cycling, and verify that Sn1 does not reappear and that temperature reads realistically.

If the error persists with a new sensor, the control pack’s sensor input circuit may be defective and a qualified spa technician should test or replace the spa pack.