A healthy gas furnace flame should burn mostly blue. If you see a yellow furnace flame that stays yellow instead of clearing, it needs a combustion inspection before you keep running the furnace.
A persistent yellow flame points to a combustion problem. That raises concern about carbon monoxide, but the flame color alone cannot tell you how much CO the furnace is producing or if it is entering your home.
What to Do Right Now
If your carbon monoxide alarm sounds, or someone in the house develops a sudden headache, dizziness, or nausea while the furnace is running, leave the house. Call emergency services or your gas utility from outside and stay out until you are told it is safe to return.
If there is no CO alarm or other immediate emergency, turn the furnace off and schedule heating repair before running it again.
Do not adjust the burners, air shutters, or gas valve yourself. We need to find out why the flame changed before anything is adjusted.
What Furnace Flame Colors Mean
A furnace can burn different colors, and each tells you about the health of the system operation. Knowing when a color means a potential system failure can ensure your family's health is safe.
- Blue: A steady, mostly blue flame is what we expect from a gas furnace.
- Yellow: A flame that stays yellow needs a combustion inspection.
- Orange: A brief orange flicker from dust or debris burning off is different from a persistent orange furnace flame, which needs to be checked.
- Flickering or unstable: A flame that moves or changes noticeably while the furnace runs needs inspection.
Do not use furnace flame color alone to decide that your furnace is safe. Combustion testing tells us what is actually happening.
Does a Yellow Flame Mean Carbon Monoxide?
A yellow flame does not prove carbon monoxide is leaking into your house. It does tell us the burner is not burning the way we expect, and incomplete combustion can produce carbon monoxide.
We test the combustion instead of judging it by color alone. That tells us what your furnace is actually producing while it runs.
Carbon monoxide has no color or smell, so you cannot rely on your senses to detect it.
What Causes a Yellow Flame
If you're asking why is my furnace flame yellow, we check the burners, combustion air, venting, gas pressure, and heat exchanger to find what changed the flame.
This is not the time to start cleaning your furnace by taking apart the burner assembly. Burner and gas adjustments belong with a trained technician.
The Cracked Heat Exchanger Case
A yellow flame by itself does not mean your heat exchanger is cracked. We have to inspect and test the furnace before making that call.
The heat exchanger is the barrier between combustion gases and the air moving through your home. A crack or other failure in that barrier needs immediate attention. If we confirm a problem, we will explain what we found and what needs to happen before the furnace is used again.
If you've noticed other signs of a failing furnace, such as repeated shutdowns or trouble heating the house, tell us when you schedule the inspection.
Carbon Monoxide Detectors
Every home with fuel-burning equipment needs working carbon monoxide alarms. Install them on each level and near sleeping areas according to the alarm manufacturer's instructions and local requirements.
Test your alarms on the schedule listed by the manufacturer and replace each unit by the replacement date or service life printed on it.
A CO alarm warns you about carbon monoxide in the home. It does not tell you why your furnace flame changed, and it does not replace a combustion inspection.
Get a Combustion Inspection from Scott Hale
If your furnace flame stays yellow or orange, we will check the combustion and find out why. Scott Hale Plumbing, Heating & Air has served Salt Lake City, Utah County, Murray, and surrounding Salt Lake Valley communities since 1984.
If the furnace has to stay off and your home is losing heat, call us for emergency heating repair. If testing finds a furnace failure that requires replacement, ask about available financing options. Schedule an appointment online to speak with one of our HVAC technicians.
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