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

Safety: Delayed ignition can be dangerous. If the noise is severe or you see flames rolling out, shut off the furnace and call a professional immediately.

Steps to check (basic):

• Visual burner inspection: With power and gas off, remove the burner access panel and inspect burners for rust, debris, or misalignment.
• Clean accessible surfaces: Use a soft brush and vacuum to remove loose dust from burner faces (do not alter orifices).
• Check ignitor position: Ensure the hot surface ignitor is properly positioned near the burner it is intended to light.

When to call a technician: Any persistent booming or banging at ignition requires professional burner cleaning and gas pressure verification.