Furnace attempts to start but shuts down with E02; inducer runs but no ignition

Safety first: Turn off power and gas before working inside the burner compartment. Allow the furnace to cool.

• Inspect the flame sensor: Locate the flame sensor rod on the burner assembly (usually a single rod with one wire). Remove the mounting screw and gently pull it out. Clean the metal rod with fine steel wool or a Scotch-Brite pad until shiny. Do not sand the porcelain. Reinstall and reconnect the wire.
• Check the hot surface ignitor: The ignitor is typically a ceramic element near the burners. Visually inspect for cracks or white spots. If cracked or broken, it must be replaced with the correct Napoleon ignitor (match voltage and style).
• Verify gas supply: Ensure the manual gas shutoff valve near the furnace is fully open (handle parallel to the pipe). If other gas appliances are also not working, contact your gas supplier.
• Observe ignition sequence: With panels in place and power restored, call for heat. Watch through the sight glass: inducer starts, then ignitor should glow, then gas valve should click and burners light. If the ignitor glows but burners never light, suspect gas valve or gas supply. If burners light but go out after a few seconds and E02 appears, suspect flame sensor or ground issues.
• When to replace: If cleaning the flame sensor and confirming gas supply does not resolve the issue, replace the flame sensor and/or hot surface ignitor. Persistent E02 after part replacement may indicate a faulty ignition circuit on the control board and requires a qualified technician.