Furnace makes loud booming or delayed ignition noise when burners light.

Safety: Delayed ignition can be dangerous. If the boom is severe, shut off gas and power and call a professional.

Steps to check (limited homeowner scope):

• Visual burner inspection: With power and gas off, remove the burner access panel and look for heavy rust or debris on burners.
• Do not attempt major burner disassembly: Cleaning and alignment of burners and orifices should be done by a technician.

When to call a pro: A licensed HVAC technician should remove and clean burners, check gas pressure, inspect the heat exchanger, and replace the ignitor if weak.