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. Just, you have to deal with inappropriate air to fuel ratio, heat exchanger blockage, and faulty vent. 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 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 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, push 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 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 of this article is sufficient. 

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

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