Yellow Nat. Gas Flames

Wasn’t sure where to put this so picked plumbing…

At today’s warranty inspection, homeowner had a weird complaint - yellow flames at her gas cooktop. Not yellowed above the grill, pure yellow out of the jets, at least that is what she described.

She says that the gas company has come out and said “WOW!! Never seen that before.” Pressure tested the gas lines and concluded that it was the cooktop. GE replaced the cooktop. She says it still happens. She ws very concerned about CO at the cooktop from the yellow flames. I explained that the blue flames are putting off CO too, that is why she should run the vent. That I didn’t feel this was a hazard, at least not in that way.

Here’s the weird part, it is completely intermittant. It may last hours or days, then go away for a while. It was not doing it while I was there - cooktop, furnaces, water heaters all pretty bright blue flames.

According to her, when it happens, the flames at the gas log fireplace change color too. So she assumes the others do as well. Husband said he would check the furnaces next time it happens.

Has anyone ever heard of anything like this or have any ideas what might cause something like this? I told them I would research it a bit. I have done many houses in this development and never seen or heard this complaint before here, or anywhere else for that matter.

Thanks in advance.


I wonder could this happen when the Dryer is on or a bath room exhaust sounds like lack of air to me .
Is this home air tight ( a new home ?)

[PDF] INDG238 Gas appliances. Get them checked Keep them safe

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NEVER use a gas appliance if you think it is not working properly. Signs to look. out for include yellow or orange flames (except for fuel-effect fires - Similar pages

Flame Fix - Gas & Oil boiler service & repair &](

Home Gas Test
Unlike asbestos or cigarettes - natural gas invades every part of our lives without our permission. From providing us with comfortable heat, to delivering delicious cooked food and protecting us from the elements of nature’s cold fury, to drying our undergarments so we can feel warm and fuzzy. Gas-waste infects us at every level of our lives.

Seeing is believing.
Try this simple test for yourself. In the evening, turn on a gas appliance. Then turn off all of the lights in the room and watch as your gas flame burns. Look for the blue colors. That’s methane gas burning. Methane gas makes up most of your natural gas supply and it burns with a blue color.
If there are yellow, orange, green, purple or red colors in your flame - that isn’t just methane gas burning. Such colors indicate that something else is burning with the methane. The industry calls them condensates. Your condensates could be Benzene, Toluene, Tar, Oil, Dust, Rust, Gas Odorants or - PCBs. Notice how the colors burst out and jump about. The colored condensates bursting in your flame are some of the hazardous chemicals in your gas.

We know - if your flame isn’t a blue color - your burning something mixed with the methane. And those non-methane combustion byproducts coming from the gas company are entering the indoor air.
Natural gas indoor environmental smoke test.
Remove wall pictures and hangings, looking for a shadow behind where the object hung. The shadow is cleaner than the surrounding surface because combustion from gas appliance flames deposits environmental smoke covering everything indoors. Objects hanging on the wall collect the gas smoke and shield the wall. And your breathing this stuff?
Look at the bottom of your pots and pans used on gas appliances. See those dark sooty smudges, that’s environmental smoke etched into the metal. These chemicals are so powerful, they eat into the metal surface and can’t be removed. Think what they are doing to your lungs.
If you have a fireplace with a gas log insert, look at the black sooty deposits coating the hard ceramic. That’s unburned hydrocarbon stains and they don’t wash off.
Using a white cloth, wash a section of the wall and ceiling around a gas appliance. Observe the yellow stuff on the white cloth, it’s unburned chemicals from your indoor gas appliances.
Gas is still the best energy choice we have. It’s cheap, it’s plentiful, and it’s a commodity fuel that needs to be cleaned up. Unfortunately, we can’t rely upon the gas utility to do it for us. We need help.


Thanks Cookie,

But how does that explain the intermittent indication of the problem? The flames were fine today when I ran it. Of course I also had all of the exhaust vents in the home going, pulling in outside air…

These houses are new and relatively tight. But have fresh air inlets and lots of visible (with IR) infiltration around poorly installed and sealed doors.

Sounds crazy, but one alternative could be the pipe dope.
Have you checked the threads.

The moisture in the air or a breeze blowing on the flames will turn them yellow. blowing on them will turn them yellow. Also if they used the wrong conversion kit or the orface is clogged it will cause this. Just my two cents

Was there a drip (dirt) leg on the piping at the stove?


The flames on most burners that use a gaseous fuel such as natural gas or liquified petroleum gas should burn steadily with a clear, blue flame, except for special designs such as fireplace logs and torches. A wavering, yellow flame on a normal gas burner indicates that the burner is out of adjustment or the air inlet is restricted. As a result, the burner may be producing excessive amounts of CO.

Good post Brian

Good information and misconceptions of CO

and as always

Plumbing is a good place for this discussion.

[FONT=TimesNewRoman]Some interesting maximum limits set by ANSI (American National Standards Institute)

• Allowed from unvented space heaters – 200 ppm
• Allowed in furnace flue gas – 400 ppm
• Allowed for emissions from an unvented gas oven – 800 ppm

• Note: All ppm limits above are for “air-free” measurements and all exceed what is considered acceptable “healthful” by all these other testing or oversight organizations.

[FONT=Verdana]Carbon monoxide (CO) concentration in Parts Per Million or as percentage of air

**Parts Per Million **

**% of CO in air **

**Inhalation time and toxic symptoms developed **

0 - 1 ppm

Normal background levels

9 ppm


Maximum allowable concentration short term in living area (ASHRAE)

25 ppm


Maximum exposure TWA (Time Weighted Average) (ACGIH) in the workplace**.**

50 ppm


Maximum exposure allowed (OSHA) in the workplace**.**

200 ppm


Mild headache, fatigue, nausea and dizziness.

400 ppm


**Serious headache - other symptoms intensify. **
Life threatening after 3 hours.

800 ppm


**Dizziness, nausea and convulsions. **Unconscious within 2 hours, dead within 2 to 3 hours.

1600 ppm


**Headache, dizziness and nausea. **
Death within 1 - 2 hours.

3200 ppm


**Headache, dizziness and nausea. **
Death within 1 hour.

6400 ppm


Headache, dizziness and nausea.
Death within 25 - 30 minutes.

12,800 ppm


**Death within 1 - 3 minutes. **

Effects can vary significantly based on age, sex, weight and overall health.

CO Busters****

Carbon Monoxide Information Center
Sponsored by First Alert - (312) 337-7773
**Carbon Monoxide Detectors - UL Standard **

"According to UL Standard 2034, home carbon monoxide detectors must sound a warning before carbon monoxide levels reach 100 parts per million over 90 minutes, 200 parts per million over 35 minutes or 400 parts per million over 15 minutes. The standard requires the alarm must sound before an average; healthy adult begins to experience symptoms of carbon monoxide poisoning. The warning provides time to evacuate the premises."

***Note: There are three organizations ASHRAE, ACGIH, and OSHA that rate levels below 100 ppm as unsafe, this is before many home UL Standard ***
CO alarms/monitors/detectors would ever sound for a potential problem.

I often find gas ranges/cooktops with recirculating fans and NO direct exhaust. Although this is allowable I think it is just plain foolish. All other gas fired appliances exhaust to the exterior somehow, except for unvented space heaters.

My experience is, “general elevation of detectable CO with yellow flames.”
You can get a fairly “dirty flame” and still be within ANSI acceptable limits.

Here in lies the problem we may run into.
I call appliance out for elevated/detectable CO emissions.
Seller/realtor gets an appliance tech to come out usually without a CO detector.
Repair person checks “by looking at the flame only” and gives a clean bill of health.
I’m stuck with egg on my face even with all of the information I can provide to the contrary.

I quit taking photos of my CO detector pegged, and just let them know fuel supplied appliance should be vented to the exterior, IMO, and have tech with CO detection adjust and repair to the current standards for that type appliance.

They call me back and say tech said it’s OK I ask "did they use CO detector. No, and there you have it, same sh!t different day.

I’ve found a thorough cleaning of all removable burner components and their ports can make a world of difference in flame color and CO emissions.

Good info Barry. Thanks.

In all normal ways this installation was decent.

It was vented to the exterior (I hate that one as well.)

It was a new appliance that she had replaced. I think the one I tested was a couple of months old.

Again, everything looked and tested correct for me. Yet the homeowners insist that this problem occurs periodically and randomly. Which eliminates the dirty jets theory and the installation problem theory - since it work correctly some of the time.

I am also curious about her reported response by the gas company, but do not know how accurate that report is.

Unfortunately, this homeowner has had several major issues with their new home and are definately on the unhappy side about it. I wonder if that might be contributing to their overall view. I personally, like the idea/theory of something in the gas the best - it fits the criteria most closely - except for the fact that I have done many other homes in the area and neighborhood and never heard or seen this problem.

I guess it will remain a mystery. Thanks for the input.

She may have the wrong orifice’s in place. Is her house on LP or Natural Gas? Appliances for LP or Natural Gas? Possible mismatch. Verify in Owners Manuals for appliances. Another possibility is too small of a supply line, to handle multiple appliances operating at the same time.

Has the utility checked the pressure regulator for the entire house? Intermittant failure could cause low pressure resulting in yellow flames.

“Since it occurs with different gas appliances, sounds like it may be an intermittent gas pressure regulator problem.”

Mentioned back in Post #7, but no response as to whether it was ever checked.