Heater locks out with F03; unit may start then shut down after a few seconds of flame.

Safety first: Disconnect power and shut off gas before opening the heater. Flame instability can lead to incomplete combustion and carbon monoxide.

• Inspect burner and orifices: Remove the burner tray from the Nirvana heater. Check for rust, spider webs, or debris in the burner ports and orifices. Clean with a soft brush and compressed air; do not enlarge orifices.
• Clean flame sensor: Locate the Nirvana flame sensor rod. Lightly polish with fine steel wool to remove oxidation. Ensure the sensor is properly positioned in the flame path.
• Check wiring and ground: Inspect the flame sensor wire from the sensor to the control board for damage or loose connections. Verify the heater chassis ground connection is tight and free of corrosion.
• Ventilation and wind: For outdoor Nirvana units, ensure the heater is not exposed to strong prevailing winds that can blow out the flame. For indoor units, verify adequate combustion air openings are not blocked.
• Professional checks: If F03 persists, a technician should verify gas pressure stability and test the Nirvana ignition control board for proper flame rectification signal.