Furnace makes loud banging or booming noise at startup when burners ignite.

Safety: Delayed ignition can damage the heat exchanger and is a fire hazard. Turn off gas and power before inspecting burners.

Steps:

• Inspect burners: Remove the burner assembly if accessible. Look for rust, debris, or spider webs in burner ports. Clean with a soft brush and compressed air.
• Check ignitor position: Ensure the ignitor is positioned so that gas flows directly across the glowing element.
• Reassemble carefully: Make sure burners are properly seated and aligned with the manifold.

When to call a technician: If booming persists, gas pressure and combustion should be checked by a professional. Do not continue operating with loud ignition bangs.