Water heater locks out with E02, fan may start but burner does not light or shuts down quickly.

Safety: Isolate power and gas before opening the casing. Allow the unit to cool.

• Check for intermittent gas supply: Verify that other gas appliances run without interruption. If they also cut out, contact the gas supplier.
• Clean burner and primary heat exchanger: Remove the burner assembly following the service manual. Brush off debris and vacuum. Inspect the primary heat exchanger fins for heavy soot or scale; gently clean with a soft brush and compressed air. Excessive soot indicates combustion issues that require a professional combustion analysis.
• Inspect flame sensor: Clean the flame detection electrode with fine abrasive and ensure it is correctly positioned in the flame envelope. Check the cable for damage and ensure a solid connection to the PCB.
• Check condensate drain (for condensing models): A blocked condensate trap can cause poor combustion and flame loss. Remove the trap, flush with water, and ensure the drain hose is not kinked or frozen.
• Reset and test: Restore gas and power, reset the appliance, and run hot water at a stable flow. If E02 reappears, the gas valve modulation coil or control PCB may be defective and should be checked by a certified Chaffoteaux technician.