Where Is The Flame Sensor On A Carrier Furnace?

Knowing the components of your furnace system will enable you to maintain it properly, and being knowledgeable about where they are located can make troubleshooting simpler. So, if you're having problems with your flame sensor, you may ask, where is it located? We searched the internet to look for answers, and here is what we discovered.  

The flame sensor appears to be a metallic rod and is placed on the burner assembly. Usually bent, it rests directly in front of the furnace's pilot flame. For your furnace to operate safely, a flame sensor is crucial.

Continue reading as we discuss the function of the flame sensor. We'll tackle the signs of a faulty flame sensor, how and when you should replace it, and how to clean it. We'll also cover the difference between a flame sensor and a thermocouple. Additionally, we'll tell you how much it costs to replace your sensor.

Furnace repair, maintenance, and troubleshooting. - Where Is The Flame Sensor On A Carrier Furnace?

What Is A Flame Sensor And Its Function?

The burner assembly houses the flame sensor, which is a furnace safety component. It keeps an eye on the unit and checks to see if a flame is burning.

All furnaces have a flame sensor, which determines whether the furnace has fired properly. It makes it easier for the gas valve and the furnace to communicate.

To prevent a potential gas leak, the furnace will be turned off if the sensor does not detect an active flame. The furnace flame sensor helps shield occupants from carbon monoxide poisoning and explosions that may happen if gas were permitted to enter the home unchecked.

How To Know If You Have A Functioning Flame Sensor?

Hispanic airconditioning repair man performing maintenance

Your HVAC specialists will troubleshoot your flame sensors during routine furnace tune-ups and inspections to guarantee appropriate performance and safe functionality, as well as to prevent more significant damage to the unit. Here is how to do it:

Cut Off Power To The Furnace

After finding the sensor, unplug the device. If it is impossible to unhook the appliance, turn off the power using the breaker in the breaker box.

Remove The Flame Sensor

Remove the screw holding the flame sensor in place using a driver or wrench, then carefully remove it.

Test The Resistance

By placing the probes of a multimeter on the white and blue wire ports on the sensor, you may demonstrate resistance. Low resistance should be picked up by the device.

Then, press the open end of the flame sensor against a test lamp or a 60-watt bulb. See if the multimeter displays a high resistance.

The flame sensor needs to be changed if the multimeter's open end is put on a light source and it doesn't detect a resistance discrepancy.

What Happens When You Have A Faulty Flame Sensor?

An HVAC technician working on a furnace unit system

In the absence of a flame sensor, your furnace will continue to release gas even when nothing is present to ignite it, leading to a dangerous gas buildup. If it is clogged or broken, it will turn off the heating system on its own if it doesn't detect a flame.

The majority of furnaces will enter a safety ignition lockout after three shutdowns. Continuously tampering with a defective furnace flame sensor can lead to problems with other furnace components and lower overall efficiency, in addition to being extremely inconvenient.

What Are The Signs Of A Faulty Flame Sensor?

The hazard of a malfunctioning furnace flame sensor is severe. It's possible for natural gas or propane to escape into your home without a functional flame sensor and to start a fire by accident. Because of this, understanding how to identify a faulty flame sensor is crucial.

Here are some signs you should look out for to know if you have a faulty flame sensor: 

Furnace Short Cycling

This is the typical sign of a malfunctioning flame sensor. When a furnace is turned on, a defective sensor fails to detect the heat it produces, which causes it to close the gas valve and turn the furnace off. 

Occasionally, a faulty thermostat may cause the furnace to short cycle. The malfunctioning flame sensor is typically to blame when the furnace runs, stops, and then restarts.

Cracked Flame Sensor

Short cycles are noticeable, but you must first locate the flame sensor to find a fracture in it. A damaged flame sensor will have a crack in the porcelain section on the outside.

That component is in charge of heat detection. Its capacity to sense heat will be severely constrained or eliminated if it is damaged.

Dirty Flame Sensor

Anything that restricts a sensor's ability to exchange heat will have unexpected results. When it comes to flame sensors, the sensor itself will either show signs of corrosion or dirt/soot.

This could be a result of normal wear and tear, excessive humidity, or inconsistent or nonexistent flame furnace cleaning. You will frequently see your furnace short cycling if the sensor loses its ability to detect heat owing to a layer of corrosion or dirt on it.

How Often Should You Replace A Flame Sensor?

Repairman with Digital Infrared Thermometer Checks Gas Furnace

The flame sensor should endure for roughly five years if you've just changed it or installed a new furnace. Since a furnace typically lasts 15 to 30 years, you should plan on replacing the flame sensor once or twice during your time as a homeowner.

Seasonal furnace maintenance and flame sensor cleaning are required to increase the sensor's longevity. Even if everything seems to be going well with the furnace, cleaning the sensor once a year will save you from needing to contact emergency heating assistance in the dead of winter.

You can read more about this in this post: How Long Do Flame Sensors Last?

How To Clean A Flame Sensor?

Technician repairing Gas Furnace.

Your nearby HVAC expert will shut off the furnace before removing the sensor from the burner assembly to clean it.

Regular flame exposure makes the sensor vulnerable to grit buildup, which must be removed by lightly sanding and wiping the surface. A sensor may need to be replaced if cleaning does not result in improved performance.

Here is a detailed step-by-step guide to cleaning your flame sensor if you want to do it yourself: 

Step 1: Turn Off Power

Make sure to shut off the gas and the furnace's electricity at the breaker box before you begin the cleaning operation. A minimum of 30 minutes should pass after the furnace has been running before undertaking the next stages.

Step 2: Find The Flame Sensor

As mentioned, you can find the sensor at the burner assembly. Look for a rod-shaped object in there. Detach the furnace access cover after that.

Step 3: Remove The Sensor From The Burner Assembly

Disconnect the wiring that connects to the sensor and control box by loosening the screws or bolts. After that, slowly remove the sensor from the bracket.

Step 4: Clean The Sensor

Scrub the metal rod lightly with emery paper or light-grit sandpaper to remove any residue and soot. Don't clean too vigorously since this could scratch or harm the sensor.

When finished, use a lint-free cloth to remove any soot accumulation.

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Step 5: Reinsert The Sensor To The Burner Assembly

Tighten the screws after reconnecting the cabling to the sensor and control box. Verify that the sensor is firmly attached to the burner unit. Reinstall the furnace access cover after that.

Step 6: Test If The Sensor Is Working

It might not be essential to replace the flame sensor if the device turns on and off correctly.

Flame Sensor Vs. Thermocouple - What's The Difference?

Furnace repair, maintenance, and troubleshooting.

Despite having many similarities, a thermocouple and a flame sensor have different properties and ways of working.


On older gas furnace models with a standing pilot, a thermocouple is frequently detected. The top of the thermocouple is kept at a high temperature by a tiny flame that burns continually.

The thermocouple will automatically shut off the gas valve for the furnace if the flame goes out and the thermocouple tip cools.

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Flame Sensor

In modern furnaces that run on an electronic ignition rather than a standing pilot light, flame sensors are used. The gas is lit by electrical igniters in these variants.

The flame sensors, as previously indicated, make sure the burners are working properly and have lit the gas. The sensor will shut off the gas if it notices that the burner has stopped working.

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How Much Does It Cost To Replace A Flame Sensor?

The price of flame sensors may differ from one company to another. When replacing the sensors, it is always preferable to pick one that is more dependable. Particularly if you're purchasing a new flame sensor, the overall cost may vary between $350 and $500.

Final Words

It is advantageous to know where your flame sensor is so that you can easily check if you suspect that it is malfunctioning. It also makes it more convenient and time-saving for you whenever you have to service or clean it. 

Before you leave, you can check out these related articles: 

Short Cycling Furnace - What To Do?

Do Electric Furnaces Have Flame Sensors?

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