Furnace makes loud banging or booming noise at startup.

Safety: Turn off gas and power. Delayed ignition can be dangerous and should be corrected promptly.

• Clean burners: Remove the burner assembly and clean each burner and crossover port with a brush and compressed air. Ensure all ports are open and free of rust.
• Check burner alignment: Reinstall burners so they are properly seated and aligned with the gas orifices and ignitor.
• Inspect ignitor position: Ensure the hot surface ignitor is correctly positioned in the gas stream and near the burner ports. Adjust if necessary.
• Professional gas adjustment: If booming persists, have a licensed technician check gas pressure and combustion settings.