3 Reasons For Gas Furnace Flame Blowback [Easy Solution]

Gas furnace flame blowback is a common incident for every furnace. But you have no reason to worry about it because we have got your back.

This article will discuss the 3 most common reasons behind gas furnace flame blowback and what you can do about them.

If you can utilise the instructions discussed in this article, you will never have to worry about gas furnace flame blowback again and won’t struggle from furnace lighting problem.

So let’s get started.

3 Causes And Solutions Of Gas Furnace Flame Blowback

You can easily solve the issue of gas furnace flame blowback. You just have to deal with inappropriate air-to-fuel ratio, heat exchanger blockage, and faulty vents. You will learn more about these issues right here. We will teach you how to get rid of such problems as well.

Check them out,

Cause 1: Fuel & Air Combination Is Not Right

A furnace burns the fire with the help of fuel and air. A perfect balance of these two elements keeps a healthy flame active. However, their ratio can get imbalanced due to the fault of the furnace. When this happens, your furnace will have flame blowback.

You will know if this is the issue by the look of the flame. The normal furnace flame is bright blue. If this flame turns red or orange, you can conclude that the air-to-fuel ratio is not okay and needs adjustment.


The perfect fuel-to-air ratio is 1:10. You have to achieve this combination to prevent flame blowback in the furnace. Here’s what you can do to fix it,

  • See if the air intake fan is working faster than usual
  • Make sure that only the proper amount of gas is being passed into the furnace
  • Adjust the air intake fan’s speed till the furnace flame turns blue
  • If adjusting the fan doesn’t work, try adjusting the gas intake valve and see if this changes the flame colour.

If you keep trying this way, you will achieve the perfect flame colour soon enough. This is what a perfect furnace flame looks like.

Cause 2: Blocked Heat Exchanger

The majority of the furnace’s function takes place in the heat exchanger. Here air, fuel, and flame come together to generate heat. In order for this heat generation to work properly, the elements involved must be pure. 

However, chlorine, fluorine, or other similar home product chemical can pollute the environment of the heat exchanger. This can greatly affect the overall heat exchanger system, resulting in a blockage. This clogged situation eventually causes blowback. 


If the blocked heat exchanger is the culprit behind the gas furnace flame blowback, you must clean the heat exchanger system. Getting rid of pollution is the goal. Here’s how it’s done,

  • Turn off the furnace system
  • Spray or apply Alkaline to the heat exchanger body
  • Rinse the heat exchanger body with a high-flow water
  • Apply Nitric acid in the heat exchanger
  • Rinse again in the same way

If you clean the heat exchanger this way, it should work just fine for at least a year. It means you will not have a gas furnace flame blowback till then.  

Cause 3: Venting System Is Faulty

A furnace generates a huge amount of residue gas as byproducts. This gas leaves the system through the exhaust vent. If the vent is not placed high enough or something gets clogged in the vent, then the gas will not escape the system.

As a consequence, these remnant gases will pile up, pushing more gases back into the furnace. This is one kind of blockage, and this can easily lead to gas furnace flame blowback. 


You have to clean the air vent of the furnace properly to ensure such blowback doesn’t occur. Here’s how to do it,

  • Turn the furnace blower on
  • Start by sweeping the dirt off the vent path
  • Turn the fan off and vacuum the vent path
  • Use the vacuum to clean the blower compartment dust
  • Replace the furnace filter in the vent

After taking care of these 5 simple steps, you will have a smoothly running furnace vent pipe, reducing the chance of furnace flame blowback.

Pro Tip:

You can prevent incidents such as flame blowbacks with your furnace annual maintenance. Once a year take the whole furnace apart and clean each part thoroughly. It will save you a lot of trouble and a lot of cash as well.

And that was all. One of these 3 causes is the reason why your furnace had to suffer a flame blowback. Find out the issue, apply our solution, and get a perfectly working furnace within an hour.


What does a bad furnace flame look like?

A bad furnace flame is orange or yellow in colour. It will not be stable and tremble frequently.

How long should you press the button in a gas furnace?

You should keep the button pressed for 30 seconds to 1 minute after the pilot lights up.

How do you adjust the flame on a gas furnace?

You can easily adjust the gas furnace flame just by twisting the adjustment screw.

Can you bypass a flame sensor on the gas furnace?

No, you cannot bypass a flame sensor on a gas furnace.

Why furnace blowback occurs?

Furnace blowback takes place mainly due to the collection of hydrocarbons in the system.

Can a gas furnace explode?

Yes, a gas furnace can catch on fire and explode. However, the chances of this happening are very slim.

Final Verdict:

If you own a gas furnace, you have to deal with a flame blowback at least once. But that will not be a problem if you know what to do in case a gas furnace flame blowback occurs. Just following the instructions in this article is sufficient. 

If you have any confusion or questions, let us know in the comment below.

About William

William is the founder of Fireplacehubs.com. He has real life practical skills in fixing smoker & heating appliance issues. He loves to share his knowledge & helps others in fixing their appliances & saving their money. William firmly believes that anyone can repair his or her unit with the correct guidance & knowledge. See more at about us.

6 thoughts on “3 Reasons For Gas Furnace Flame Blowback [Easy Solution]”


    • Hi Randy

      Your furnace is not getting enough airflow. It’s getting overheated and triggers the reset button to trip. Clean the air filter. Or you can replace it if required. Ensure proper airflow by keeping the air vent open.


  2. Hello,all of sudden my furnace “BOOMS” when the burners ignite.I installed a NEW GAS VALVE and air filter-NO DIFFERENCE.The heat exchanger looks like new,everything IN the furnace is super clean.I have a GOODMAN 90% furnace and its impossible for my exhaust vent to be clogged.Ive watched more HVAC videos on this problem and still have no clue how to solve this problem.I DO NOT believe my Heat exchanger is BAD/CRACKED.Every step that happens in the furnace “CALL FOR HEAT” and so on functions exactly as its suppose to.What the Hell is wrong/whats left to check/fix??Please Help.Thanks.

  3. I have a gas furnace that has blow back only when it ignites nothing after that , do you have any solutions or possible cause. I have cleaned the igniter and flame senser and cleared the drain lines. also I installed a new air Filter

    • Hi Roderick

      In most cases, a gas furnace flame blows back due to an inappropriate air-to-fuel ratio, heat exchanger blockage, or faulty vent.

      Well, to fix the problem, check all the issues one by one to find out the main culprit behind the flame blowback.

      Then, try to fix it following our solution guide in the article.

      Hopefully, your problem will be solved.

      Wish you all the best!


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