The burners are the "business end" of your furnace. These shockingly simple components are the final step in the combustion process, where the correct ratio of air and fuel mix to produce heat for your home. A typical modern single-stage furnace uses a horizontal burner assembly composed of multiple individual burner units.
Each burner effectively acts as a nozzle, taking a pre-metered amount of natural gas and pushing it toward the combustion chamber. Once at the end of the burner, the gas mixes with air and ignites, producing energy the heat exchanger can extract to warm your home. However, despite their relative simplicity, furnace burners are still a common source of issues.
How Do Your Furnace's Burners Work?
In addition to the burners, two other critical components come into play when your furnace lights: the igniter and the flame sensor. While the igniter's role may be obvious, the flame sensor can be slightly more obscure. This device proves that your furnace's burners have successfully ignited, an essential step to prevent gas leaks from unlit burners.
Despite standard furnaces containing multiple individual burners, a typical furnace only has a single flame sensor and igniter. A typical configuration places the igniter at one end of the burner assembly and the flame sensor at the other. Channels in the burner assembly mean that once the first burner ignites, the rest will follow one after another.
This design means the flame sensor only needs to prove ignition on the final burner. If the final burner ignites, the other burners in a line before it must have also ignited. Conversely, an issue that prevents one or more burners from igniting usually stops the final burner from lighting, and the furnace's flame sensor will trigger a shutdown.
Why Do Burners Fail?
Burner failures typically result from underlying physical problems. Most burner and burner assemblies are metal, so rust is a common problem. Issues that result in incomplete or inefficient combustion can also create excessive soot, which can clog the orifices in the burners and prevent complete or consistent ignition.
Other issues include clogs in the channels between burners. These problems may technically not prevent the burners from working, but they will prevent the flame from igniting burners further down in the assembly. As a result, the flame sensor will fail to detect a flame on the final burner in the line and your furnace will shut down.
Burner issues can range from relatively minor problems that only require cleaning to more substantial issues that require an HVAC technician to replace the entire assembly. Depending on your furnace's design, you may also be able to replace individual burners. Since burners deal with the furnace's gas supply, the safest option is to allow a professional to conduct these repairs.
For more information on furnace services, contact a professional near you.