How-To Guides
Where is the Location of the Flame Sensor on a Furnace?
AAZparts Team
Updated on May 26, 2025
6 min read
The flame sensor is a crucial component in a furnace system, ensuring safety and efficient operation by detecting the presence of a flame. Knowing the exact location of the flame sensor in your furnace not only makes it easier to inspect and maintain but also allows for timely troubleshooting of related issues. In this article, let’s explore with AZParts where the flame sensor is located in a furnace, as well as how to identify and properly maintain this device to keep your furnace running smoothly and safely.
1. What is a Furnace Flame Sensor?
The flame sensor is a critical safety component in gas furnaces. Its primary function is to detect whether a flame is present after the ignition system activates. If no flame is detected, the sensor sends a signal to the control board to shut off the gas supply, preventing dangerous gas leaks that could lead to fires, explosions, or toxic gas buildup.
When the furnace starts, the gas valve opens, and the ignition system creates a spark to ignite the gas. The flame sensor detects the presence of the flame through a small ionization current generated when the flame comes into contact with the sensor tip. If the sensor fails to detect a flame within a few seconds, the system automatically shuts off the gas for safety.
The flame sensor is a critical safety component in gas furnaces (Source: AZParts) .
2. Where is the Location of the Flame Sensor on a Furnace?
The flame sensor is usually located near the burner assembly in a gas furnace, the area where the flame is produced. It is a small, thin metal rod mounted on a bracket that extends into the flame to detect its presence when the furnace is operating.
To accurately locate the flame sensor:
- Turn off the power and shut off the gas supply before inspecting.
- Open the furnace cover and locate the burner assembly.
- The flame sensor typically appears as a small, curved metal rod with a wire connected to the control board. It is positioned right in the flame area or near the ignitor.
If replacement is needed, be sure to choose a sensor compatible with your furnace model to ensure proper performance and safe operation.
The flame sensor is usually located near the burner assembly in a gas furnace (Source: AZParts)
3. Signs of a Bad Flame Sensor Symptoms in Your Furnace
A dirty, oxidized, or faulty flame sensor can cause various issues during the operation of a gas furnace. Here are some common signs indicating that the flame sensor may be malfunctioning:
- The furnace starts but shuts off after a few seconds: This is a typical sign that the sensor is not detecting the flame. Even though the flame is burning, the sensor fails to send a confirmation signal, causing the system to automatically shut off the gas for safety.
- The furnace won’t start: If the sensor is completely damaged, the system will not open the gas valve because it does not receive the signal ensuring that the flame will ignite, preventing the furnace from operating.
- Error lights blinking or error codes displayed on the control panel: Most modern furnaces have error display functions. If the sensor malfunctions, the system may show error codes related to flame detection failure or gas shutoff.
- Unstable furnace operation: The furnace may cycle on and off repeatedly, especially during peak usage times. This not only reduces heating efficiency but also shortens the equipment’s lifespan.
- Reduced heating performance and increased fuel consumption: Frequent restarts caused by a faulty sensor can waste fuel and increase energy bills.
If you notice any of these signs, it’s important to inspect and clean the flame sensor. If the sensor is old or severely damaged, replacing it with a compatible new one will help ensure your furnace runs safely and efficiently.
A dirty, oxidized, or faulty flame sensor can cause various issues during the operation of a gas furnace (Source: Freepik)
4. How to Properly Clean a Furnace Flame Sensor
To keep your furnace operating safely and efficiently, regular cleaning of the flame sensor is essential. A dirty or oxidized sensor can cause the furnace to malfunction or shut off unexpectedly. Below are the proper steps to clean the flame sensor that you can follow and perform:
4.1. Cut the power
Before starting to clean the flame sensor, you must ensure complete safety. Turn off the power supply to the furnace entirely and close the gas valve if possible. This precaution helps prevent risks of electrical shock, gas leaks, or fire during the maintenance process.
4.2. Remove the flame sensor
Open the front panel of the furnace to access the burner assembly. The flame sensor is usually a small metal rod located near the ignitor and positioned toward the flame. Use a screwdriver to remove the screws securing the sensor, then gently pull the sensor out of its place. Be careful not to bend or damage this component.
4.3. Clean off debris
Use fine-grit sandpaper (between 180 and 220 grit) or a soft, dry cloth to clean the metal part of the sensor. Gently rub in one direction to remove dust, soot, and oxidation from the surface. Avoid using water, chemicals, or sharp objects, as these can damage the sensor or affect its heat conduction ability.
4.4. Reattach the flame sensor
After cleaning, reinstall the sensor in its original position and securely tighten the screws. Close the furnace panel, restore the power supply, and open the gas valve. Start the furnace and check that it operates steadily without sudden shutoffs or sensor errors. If everything runs smoothly, the cleaning process was successful.
It’s recommended to clean the flame sensor 1 to 2 times per year, especially before the cold season or if you notice unstable furnace operation. If problems persist after cleaning, the sensor may be faulty and require replacement. In that case, you can consider quality flame sensors from AZParts to ensure durability and optimal performance.
How to Properly Clean a Furnace Flame Sensor (Source: AZParts)
5. What is the average Lifespan of a Flame Sensor?
The average lifespan of a flame sensor in a furnace typically ranges from 5 to 10 years, depending on its quality, usage conditions, and regular maintenance. Frequent cleaning and operating the furnace in a clean environment can help extend this lifespan. However, buildup of dust, soot, or exposure to moisture can significantly reduce its durability. When the sensor shows signs of poor performance or frequent errors, replacing it promptly is recommended to maintain safe and efficient furnace operation.
Knowing the exact location of the flame sensor makes inspection and maintenance easier, enhancing both performance and safety. Regular cleaning and upkeep not only extend the sensor’s lifespan but also help prevent unexpected malfunctions. We hope this article has provided helpful insights to support safe and efficient furnace operation. If you're looking for replacement parts or upgrades, explore our selection of AZParts’ furnace parts to keep your system running smoothly.
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