State tankless water heater shuts down with E02 shortly after ignition; burner lights briefly then goes out.

Safety: Turn off power and gas before servicing. Allow the unit to cool.

• Inspect flame sensor: Remove the front cover. Locate the flame rod (often combined with the igniter). Clean the rod with fine abrasive pad to remove oxidation. Ensure the ceramic insulator is intact.
• Check ground: Verify the green ground wire from the heater chassis to the electrical supply ground is secure and not corroded. Tighten any loose chassis ground screws.
• Gas pressure under load: If you have a manometer and are qualified, verify inlet gas pressure while the unit is firing. Compare to the State specification on the rating plate. If pressure drops below spec, contact a licensed gas fitter.
• Wiring and board: Inspect the harness from the flame sensor to the control board for damage or loose connectors. Reseat connectors. If E02 continues, the control board flame detection circuit may be defective and should be tested/replaced by a technician.