Burner flame appearance check

What is going on

Check the flames with the burner compartment door installed. Flames should be stable, quiet, soft and blue. Dust can cause orange tips, but the flames must not be yellow. Flames should extend straight out of the burners without curling, floating or lifting off, and must not touch the sides of the heat exchanger firing tubes.

Likely causes

• Flame lifting or floating from burner ports
• Yellow flame from incomplete combustion

Check in this order

1. Turn the furnace on at the thermostat and wait a few minutes for dust to clear.
2. Check that the flames are stable, quiet, soft and blue.
3. Check that the flames extend directly out and do not curl, float or lift off.
4. Check that no flame touches the sides of the firing tubes.
5. If a flame looks abnormal, contact a qualified service agent at once.

More furnace guides

• Airflow lower than demanded, furnace runs on low stage when high stage is expected
• Alternate combustion air opening (upflow or horizontal)
• Alternate vent/flue location (upflow or horizontal left)
• Annual inspection checklist
• Auxiliary limit control (location and purpose)
• Auxiliary limit switch open (blower compartment)