How To Fix Yellow Flame On Gas Furnace

Have you encountered a yellow flame on gas and didn’t know what to do? Well, you’re in the right place! You need to know that if the fuel to air ratio is correct, a gas burner will burn blue. 

A yellow burner flame indicates that there isn’t enough air available for complete gas combustion. To remedy this issue, you must adjust the burner’s air shutter to allow more air in, which a skilled do-it-yourselfer can accomplish.

You may be wondering what your next move should be if you have a gas furnace with a yellow flame. 

Here are some tips on how to fix the issue and return your system to normal.

  1. Check for clogs in the vent or disconnects that can cause flames to burn yellowish-orange. If there is no obstruction, then check for dirty filters; clean as necessary.
  2. Perform an annual maintenance inspection of the heating system and ensure it is working properly according to the manufacturer’s specifications; this includes checking thermostat settings and pressures.
  3. Consider installing a new high-efficiency filter (not just replacing your old one).

Is My Furnace Supposed to Have a Flame?

A healthy natural gas furnace flame has a roaring blue flame with a small pale blue triangle in the center. There may be a tiny yellow tip. A blue flame indicates that the gas is being burned safely and effectively, implying that it is not wasted.

A yellow flame is not normal for a gas furnace. The only time the combustion chamber has to be lit with an open flame is when there is no natural gas supply. This means that you are trying to light your system manually. 

If that’s what’s happening, then the problem must lie elsewhere in your system. A lot of times, this happens after power outages or surges. This can damage components inside furnaces and cause them not to work correctly again until they’re replaced.

How Should a Furnace Flame Look?

A furnace flame should be yellow. If the flame is orange or if it has black spots, that means there are problems with your gas furnace. You will likely get poor quality heat and increased energy costs until you get this fixed. Luckily, there are a few things you can try to fix the problem yourself.

First, check your pilot light by turning off all of your gas furnace’s controls and then turn it on again. This should reignite the pilot light so that you get more heat from your device for energy costs. 

If this does not work, call someone experienced with furnaces because there could be something wrong with your equipment or something blocking airflow in the system. 

However, you may need an HVAC professional if these steps do not solve the problem.

What Does a Yellow Furnace Flame Indicate?

A yellow furnace flame is a sign that your heat exchanger or burner is dirty. It may also be due to excess carbon in the air supply, gas pressure problems, low airflow through your vent system, or improper combustion settings on your thermostat.

Therefore, it’s important to fix your yellow furnace flame as soon as possible. If you let the problem go, it will only worsen and eventually lead to more expensive repairs or system replacements.

In case you want to fix the problem of a yellow flame yourself, here’s what you need to do:

  1. Allow the stove to cool, remove the top grates and lift the stovetop to reveal the burner piping. On most stoves, the air shutter is located just behind the burner gas valve. It’s a sliding plate or tube covering the burner air vent and is easily adjustable. 
  2. Remove the retaining screw that holds the shutter in place. 
  3. Open the shutter gradually, turning on the burner all at once until it turns blue. 
  4. Re-attach the set screw
  5. Switch off the burner
  6. Finally, replace the stovetop top grates before turning them off completely.

How to Adjust Flame on Gas Furnace

To appropriately adjust the flame on a gas furnace, you should:

  1. Turn off the main gas supply.
  2. Locate the manual emergency shutoff valve found on or near your furnace. If you cannot find it, turn off all of the individual valves that run to your system one by one until you locate it.
  3. Turn this knob clockwise until it stops and then counterclockwise about a quarter of an inch for natural gas furnaces, or half an inch if using LP (liquid propane). 

This should stop any further fuel flow through the line while still allowing oxygen to support combustion. Most burners require three to five seconds at maximum adjustment before reaching optimal flame levels. The blue cone tip will retract into the burner head when adjusted correctly.

What Causes Flame Rollout on a Furnace?

A rollover can be caused by too little or too much air getting mixed in, which causes an excess of fuel. This leads to a lack of oxygen needed for combustion. Therefore, it results in a ‘flame rollout’ where the fire goes completely out until someone notices.

To fix this issue, ensure your filters are clean, so there isn’t dust building up at any point outside the unit. That’s because this may compromise airflow into/out of registers throughout your home.

Ensure all vents are open inside each room as well! This may require some trial-and-error testing but once properly set, everything should run smoothly again.

What Should the Gas Pressure Be on a Furnace?

The gas pressure on a furnace should be within the manufacturer’s recommendations. If it is too high, your furnace may have a yellow flame instead of blue. 

You can tell if you have a problem with the gas pressure because the smell coming from the vent will be different than normal. Also, there could be water around your unit, indicating that there is insufficient combustion in the appliance to burn off residual condensate. 

This may cause an acidic build-up on internal components such as heat exchanger tubes or burner parts. The quickest way to check for this is by disconnecting one side of your dual fuel system (pilot) while leaving both lines connected downstream at the outdoor shutoff valve (gate). 

But on the inside, make sure all windows are closed during this test to avoid gas leaking into your home. If you have a yellow flame, adjust the gas pressure to meet the manufacturer’s recommendations. 

Adjust Gas Pressure on a Furnace

  1. To adjust the gas pressure on a furnace, all you need to do is:
  2. Turn off the power to the furnace at your furnace’s circuit breaker.
  3. Open up the casing of the gas valve 
  4. Locate a small screw that is connected to an adjusting nut below it. You can do that by using a flashlight or opening up another access panel on top of the main one.
  5. Use a wrench to turn clockwise for higher pressures and counterclockwise for lower ones accordingly.
  6. Once you’ve determined the right amount needed after testing, ensure you tighten everything back in place with screws before turning your power back on.


Overall, fixing yellow flame on a gas furnace is a task that anyone can complete. However, replacing the thermocouple is something even beginners with no prior knowledge of this process will succeed. 

The information provided in this post is meant to help guide you with the proper steps to fixing yellow flames on gas furnaces. 

If you have any questions or feedback regarding this post, feel free to reach out to us through email, and we’ll be happy to help.