Display shows COL or COOL; spa will not heat until water warms up.

Safety first: Ensure the spa is filled and all drains are closed before running pumps.

• Step 1 – Verify water temperature: Use an external thermometer to confirm the water is very cold (near freezing or just filled from a cold source). COL is normal in this case.
• Step 2 – Allow circulation: Run the pumps on low speed to circulate water. As the water warms slightly, the control will allow the heater to engage and COL will clear automatically.
• Step 3 – Check sensor accuracy: If the water is not cold but COL remains, compare the displayed temperature to an external thermometer. A large difference suggests a faulty temperature sensor.
• Step 4 – Inspect sensor and wiring: With power off, inspect the temperature sensor on the heater tube and its wiring to the control pack. Reseat the connector.
• Step 5 – Replace sensor if needed: If the sensor is misreading low, replace it with a Nordic-compatible temperature sensor.