Display shows COL or COOL, heater does not run, spa indicates water is too cold to heat normally.

Safety first: Ensure GFCI protection is working properly before leaving the spa powered in freezing conditions.

• Verify actual water temperature: Use an external thermometer to compare with the displayed temperature. If the display is far off, the sensor may be faulty.
• Allow water to warm gradually: If you just filled with very cold water, leave the cover on and allow the spa to run. The COL message should clear as the water warms.
• Check circulation: Confirm that the circulation pump is running and that water is moving through the heater. Poor circulation can prevent proper temperature sensing.
• Inspect temperature sensor: If the spa remains in COL mode despite warm water, inspect and, if necessary, replace the water temperature sensor.