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

Safety: Delayed ignition can be dangerous. Turn off power and gas before inspecting burners. If the noise is severe, stop using the furnace until inspected by a professional.

Steps (basic homeowner checks):

• Visual burner inspection: Remove burner access panel and visually inspect burners for rust, debris, or misalignment. Do not modify or drill burner ports.
• Check ignitor position: Ensure the hot surface ignitor is properly positioned in front of the burner where ignition should start. If it appears cracked or eroded, have it replaced.
• Do not adjust gas: Do not attempt to adjust gas pressure or orifices yourself.

Recommendation: A qualified HVAC technician should remove and clean burners, verify gas pressure, and confirm proper ignition timing on Concord furnaces with this symptom.