Dealing With Furnace Problems

They See Me Rollin' – The Causes And Symptoms Of Furnace Flame Roll-Out

19 January 2023 by Eliza Chapman

Gas furnace manufacturers carefully design their heaters to provide safe and efficient heat for your home. Since natural gas combustion produces harmful byproducts that can be toxic or even deadly, it's crucial to address any issues that may allow these chemicals to enter your home. While most furnace problems won't create a safety hazard, flame roll-out is a notable exception.

If you're unfamiliar with the term, flame roll-out refers to any condition where your furnace's flame "escapes" the furnace's combustion chamber. Once this occurs, combustion gases can seep into your home instead of being pulled through your exhaust flue. This situation can create a genuine hazard for you and your family.

How Can You Recognize the Signs of Flame Roll-Out?

The good news is that it's extremely unlikely for a flame roll-out to go unnoticed or for the problem to continue long enough to present a hazard, at least on modern furnaces. Modern furnaces will typically include several flame roll-out switches throughout the furnace interior. These switches detect the presence of a flame outside of the combustion chamber and trigger an emergency shutdown.

Thanks to these switches, the most common symptom of flame roll-out is short cycling. The furnace will shut down when it detects flames outside the combustion chamber, causing your heat to shut off before it can satisfy your thermostat's setpoint. The furnace will likely try again after a "cooldown" period, so you may notice your furnace starting and stopping repeatedly.

You can often check for the underlying cause of a short cycle by seeing if your furnace displays any error codes and cross-referencing them with your owner's manual. You can also (carefully!) open your furnace's cabinet and watch the flames; if you can see the flames outside the combustion chamber, you have a problem. Stop using your furnace immediately if you have any reason to suspect a flame roll-out.

Why Does Flame Roll-Out Happen?

Like any other combustion process, natural gas combustion requires a precise ratio of fuel and oxygen for a clean and efficient burn. However, insufficient oxygen near the burners will prevent complete ignition, allowing gas to escape into the combustion chamber. This situation allows the flame to roll out of the combustion area and ignite inside the furnace cabinet.

There are numerous reasons why there may not be enough oxygen near the burners. However, the most common causes are issues that allow combustion byproducts to remain in the combustion chamber. Damaged heat exchangers, obstructed exhaust flues, or inadequate air supply are some common reasons. These issues may or may not trigger other safety switches before roll-out occurs.

Because flame roll-out is such a dangerous problem, it's not an issue you should attempt to diagnose and solve yourself. Unlike other furnace problems, the underlying cause is unlikely to be as simple as a clogged air filter. Instead, you should always contact a trained HVAC professional to find and repair the problem so you can resume (safely) using your furnace. 

Speak to a furnace repair service to learn more.

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