Symptoms
- Black soot visible on or around the burner assembly
- Yellow or orange flame instead of a steady blue one
- Possible faint burning or odd smell near the unit
- Flue or vent connector may also show sooting
Likely causes
- CommonDirty or dusty burner reducing proper air mixingAccumulated dust and lint around the burner disrupts the clean air-to-gas ratio needed for full combustion.
- CommonInsufficient combustion air supply to the unitA tightly sealed or poorly ventilated closet starves the burner of the air it needs to burn cleanly.
- PossibleVenting problem causing exhaust gases to linger or backdraftA blocked or disconnected vent can cause incomplete combustion and soot buildup.
- PossibleBurner orifice or components damaged or misalignedPhysical damage to burner components can disrupt the flame pattern.
What to do
- Turn off the gas control to the unit before doing any inspection or cleaning.
- Visually check the flame color if you can safely relight briefly per manufacturer instructions; it should be blue with maybe a small yellow tip, not consistently yellow or orange.
- Check that the combustion air openings to the closet or space aren't blocked by stored items or dust buildup.
- Gently vacuum visible dust from around the burner area with the gas off, without disturbing internal components.
- Inspect the vent pipe connections for gaps, disconnection, or visible soot staining, which indicates exhaust isn't leaving properly.
- Do not attempt to disassemble or deeply clean the burner assembly yourself; that's a job for a technician given the combustion safety implications.
Tools and parts
- Vacuum with a hose attachment
- Flashlight
When to call a pro
Have a licensed plumber or gas technician clean the burner assembly and check the venting and combustion air supply properly.
Safety
Use caution
Sooting and yellow flames indicate incomplete combustion, which can produce carbon monoxide; if you have any symptoms of CO exposure or a CO alarm has sounded, treat it as an emergency.