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

Safety first: Turn off all power to the spa at the GFCI breaker and verify with a non-contact voltage tester before opening any panels. Water and electricity are a lethal combination.

Step-by-step:

• 1. Power cycle the spa: Turn the GFCI breaker OFF for 2–3 minutes, then back ON. If Sn1 clears and does not return, it may have been a transient error.
• 2. Inspect the sensor cable: Remove the equipment access panel. Locate the primary temperature sensor (usually threaded into the heater tube on the PDC Spas control pack). Follow its cable to the main circuit board. Check for cuts, pinches, rodent damage, or melted insulation.
• 3. Check sensor connection: Gently unplug the sensor connector from the control board, inspect for corrosion or bent pins, then firmly reconnect. Do not pull on the wires; grasp the plug body.
• 4. Inspect sensor in heater well: Verify the sensor is fully seated in the heater tube or threaded port and not loose. Look for signs of leakage or scale buildup around the sensor body.
• 5. Compare water temperature: With power restored, compare the displayed temperature to an accurate thermometer in the spa water. If the reading is wildly inaccurate or Sn1 returns, the sensor is likely defective.
• 6. Replace the sensor if needed: With power OFF and water level below the sensor port (if it threads into the plumbing), unscrew or pull the sensor from the heater tube. Install a compatible PDC Spas temperature sensor, using new O-rings or sealing gaskets as supplied. Tighten snugly but do not overtighten plastic threads.
• 7. Refill/bleed and test: Restore water level, bleed air from the heater union if needed, restore power, and verify that Sn1 is cleared and heating resumes.

When to call a technician: If a new sensor does not clear the Sn1 code, the issue may be on the PDC Spas control board sensor circuit and should be diagnosed by a qualified spa technician.