The display shows 'COOL', and the spa will not heat to the set temperature immediately after a refill or long standby.

'COOL' is typically an informational message indicating the water is significantly below the set temperature.

• Verify water level and flow: Ensure the spa is properly filled and filters are clean.
• Allow time to heat: Close the cover and allow several hours for the heater to bring the water up to temperature. Large Artesian spas can take 12–24 hours to reach the setpoint from cold.
• Check for actual heating: Confirm that the heater indicator is on and that the water temperature is slowly rising over time.

If 'COOL' persists and the water does not warm, troubleshoot as a no-heat condition (heater, sensors, or control board).