Display shows COL or COOL; heater may run continuously until set temperature is reached.

Safety: Ensure all jets and valves are open to allow proper circulation while heating from a cold start.

• Normal after refill: If you have just refilled the Hydropool spa with cold water, COL is normal. Allow the spa to heat with the cover closed; this may take many hours.
• Verify sensor reading: Compare the displayed temperature with an external thermometer. If they match, no fault exists.
• Check for flow issues: Make sure filters are clean and the circulation pump is running; poor flow can slow heating and keep the spa in COL longer.
• Sensor fault: If the display shows a very low temperature but the water feels warm, inspect and test the temperature sensor as described in Sn1.