Furnace runs but makes loud booming or delayed ignition noises when burners light.

Safety first: Delayed ignition can damage the heat exchanger and cause fire hazards. Turn off gas and power before servicing burners.

• Clean burners: Remove burner assembly and clean each burner with a wire brush. Clear rust and debris from ports.
• Check burner alignment: Ensure burners are properly seated and aligned with the igniter and flame sensor.
• Inspect for cracks: Replace any burner that is cracked or severely corroded.
• Have gas pressure checked: A licensed technician should verify manifold and inlet gas pressures and adjust or replace the gas valve if needed.