Furnace makes loud banging or booming noise at startup.

Safety warning: Delayed ignition can damage the heat exchanger and cause unsafe combustion. If bangs are severe, shut off the furnace and call a professional.

Basic checks:

• 1. Listen and observe: Watch the ignition sequence through the sight glass. If gas seems to accumulate before ignition (whoosh or boom), do not continue to run the furnace.
• 2. Inspect burners (power off): Remove the burner assembly cover. Look for rust, debris, or misaligned burners. Do not attempt to disassemble gas piping.

Professional service recommended: A technician should remove and clean the burners, verify ignitor condition, and check gas pressure and ignition timing on your Philco furnace.