Furnace makes loud banging or booming noise at startup.

Safety: Delayed ignition can be dangerous. If bangs are severe, shut off gas and call a professional.

• Visual burner inspection: With power and gas off, remove burners and inspect for rust, debris, or spider webs. Clean with a soft brush and compressed air outdoors.
• Check burner alignment: Ensure burners are properly seated in the manifold and aligned with the hot surface ignitor.
• Inspect ignitor: A weak or slow-heating ignitor can cause gas buildup. Replace if cracked or if ignition is visibly slow.
• Professional gas check: A technician should verify gas pressure and combustion to ensure safe operation.