F08 error appears; heater may start but shuts down quickly, often in cold weather.

Safety first: Turn off power before accessing sensors. Protect the heater from freezing conditions.

• Verify water temperature: Compare the pool/spa water temperature with the reading on the Nirvana display. If they differ significantly, suspect a sensor issue.
• Locate freeze sensor: Some Nirvana models use a dedicated freeze protection sensor on the manifold or inside the cabinet. Inspect its wiring and mounting.
• Check for air pockets: Ensure the heater is fully flooded with water and that there is no trapped air in the heat exchanger that could cause false low readings.
• Sensor test: Measure resistance of the freeze sensor and compare to the manufacturer’s chart. Replace if out of spec.
• System protection: In very cold climates, consider running the pump continuously or winterizing the heater to avoid freeze conditions.