F9 displayed, spa may not heat and may show erratic temperature readings

Safety first: Disconnect power at the breaker before working on sensors or the control pack.

• 1. Power reset: Turn breaker OFF for 5 minutes, then ON. If F9 returns, continue.
• 2. Locate both sensors:
  • Identify the water temperature sensor and the high-limit sensor on or near the heater tube.
  • Both typically plug into the control board with similar connectors.
• 3. Inspect and reseat connectors:
  • Unplug each sensor from the control board one at a time and reconnect firmly.
  • Check for corrosion or moisture on the connectors.
• 4. Check sensor placement:
  • Ensure both sensors are fully inserted into their wells or clamped securely to the heater tube as designed.
• 5. Replace suspect sensors:
  • If one sensor shows obviously incorrect temperature compared to actual water temperature, replace it with a Wellis‑approved part.
  • In some cases, replacing both sensors as a matched pair is recommended.
• 6. If F9 persists after sensor replacement: The control board’s sensor reading circuitry may be faulty. Have a technician test and replace the control pack if necessary.