E3 code, furnace starts inducer but burners never light, then shuts down

Safety first: Turn off electrical power and shut off the gas valve to the furnace before servicing ignition components.

• Step 1 – Verify gas supply: Ensure the manual gas shutoff valve near the furnace is in line with the pipe (open). Confirm other gas appliances in the home operate normally.
• Step 2 – Inspect hot surface ignitor: Remove the burner access panel. Locate the ignitor (usually a silicon carbide or silicon nitride element mounted near the burners). Check for cracks, white spots, or breaks. Do not touch the element with bare fingers.
• Step 3 – Check ignitor wiring: Ensure the ignitor plug is fully seated on the Ducane control board or harness and that wires are not frayed or burned.
• Step 4 – Clean flame sensor: Locate the flame sensor rod on the opposite side of the burner assembly. Remove the mounting screw and gently clean the rod with fine steel wool or an abrasive pad until shiny. Reinstall firmly.
• Step 5 – Restart furnace: Restore gas and power, then call for heat. Watch through the sight glass: inducer starts, ignitor glows, gas should flow, and flame should appear. If ignitor never glows or flame appears briefly then goes out, further testing of the ignitor resistance and gas valve coil voltage is needed.
• Step 6 – Professional service: Replacement of the gas valve or live-voltage testing at the ignitor should be done by a licensed HVAC technician.