Display shows COL or COOL and heater does not run; spa may be in freeze-protection or cool-down mode.

Note: COL is usually informational, not a fault.

• Check actual water temperature: Use a separate thermometer to confirm the water temperature.
• Verify set temperature: Ensure the set temperature on the topside is higher than the current water temperature.
• Allow cool-down: After heavy use, the spa may run pumps without heat to cool the heater. Wait 15–30 minutes and see if normal heating resumes.
• Inspect cover and environment: In very cold weather, ensure the cover is in good condition and the spa cabinet is closed to help maintain temperature.

If COL remains and the spa never heats despite correct settings and normal sensor readings, have a technician check the temperature sensor calibration and control board logic.