Although small in size, the flame sensor in your furnace plays a big role in household comfort and safety. Besides preventing your heater from short cycling, this safety component also reduces the risk of house fires by shutting down the system if it detects any sudden changes in the flame. A bad flame sensor results in wasted energy and an increased risk of house fires. How do you know if the flame sensor has gone bad? We have created an outline of tips to help you detect a malfunctioning flame sensor in your heating system.
Quick Answer: How Do I Know If My Flame Sensor Is Bad?
Signs of a bad flame sensor include short cycling, the furnace not turning on, clicking sounds, a dirty sensor rod, or a cracked porcelain housing. In many cases, the flame sensor just needs cleaning, but if the problem continues, it may need replacement.
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What Is the Purpose Of a Flame Sensor?
A flame sensor is a safety device that detects the presence of an open flame. If the component doesn’t detect a flame, the pilot light is not lit. An unlit pilot light causes the gas valve to close to shut off the gas supply, preventing potential gas leaks and fires. The flame sensor also saves energy by shutting down the furnace when no flame is present. This prevents your heater from repeatedly running partial cycles without heating your home.
Signs Of a Malfunctioning Flame Sensor
Here are the main signs that the flame sensor in your furnace has gone bad and needs maintenance:
- The heater doesn’t turn on
- Short cycling. When the heater turns on but doesn’t stay lit for full heating cycles.
- Your furnace makes an intermittent clicking sound
- The flame sensor is noticeably dirty
- A crack forms on the porcelain exterior of the flame sensor
Can You Run Your Furnace With a Bad Flame Sensor?
No. A bad flame sensor will cause your furnace to shut off as a safety precaution. This can lead to short cycling, no heat, and increased wear on your system. If your furnace keeps turning off, you should have the flame sensor inspected and cleaned or replaced.
Where Is the Flame Sensor Located?
Although every furnace is different, most flame sensors are located in the same place. Unscrew and pull back the cover on your heating system to get a better view of its internal components. Locate the burner assembly at the bottom of the furnace on its front side. Once you see a small metal box, open it up. The flame sensor is a metal rod with a porcelain exterior that is usually white in color. The flame sensor is located near the pilot light.
What Causes the Flame Sensor to Go Bad?
The most common cause of a bad flame sensor is dust buildup. Other causes include:
- Sediment buildup
- Damaged electrical wiring
- Rust and corrosion
- Cracks or breaks
How Long Does a Furnace Flame Sensor Last?
Most flame sensors last 3–5 years before needing replacement, but they often need cleaning every 1–2 years due to dust and carbon buildup.
How to Clean a Flame Sensor
The easiest way to prevent a bad flame sensor in your furnace is to continuously hire a professional to clean the component. Follow these main cleaning steps to get the device up and running again in no time:
- Turn off the heater
- Take out the flame sensor
- Remove any dust or sediment buildup
- Apply cleaning solvent to the rod
- Re-insert the flame sensor
- Restart the heater
If cleaning the flame sensor doesn’t fix the problem, you probably need to replace it with a brand new one. Schedule an appointment with Fenwick Home Services, and one of our licensed technicians will come to your home at a time that’s convenient for you to replace the flame sensor.
Furnace Repair & Replacement Services in Jacksonville, FL
If your furnace turns on and then shuts off, a dirty or failing flame sensor could be the cause. This is a common furnace issue, and in many cases, it can be fixed quickly. Our HVAC technicians can inspect, clean, or replace your flame sensor to restore heat and keep your system running safely. Schedule your furnace repair today.
Flame Sensor FAQ
Can I clean a flame sensor myself?
Yes, but you must turn off power to the furnace first. Many homeowners use a soft cloth or fine sandpaper to gently clean the metal rod.
What happens if I don’t fix a bad flame sensor?
Your furnace will continue to shut off, and eventually, you may have no heat.
How long does it take to replace a flame sensor?
Most flame sensor replacements take 30–60 minutes.
Why does my furnace turn on then shut off after a few minutes?
This is usually caused by a dirty or failing flame sensor that cannot detect the flame properly.
Is a flame sensor the same as a thermocouple?
No. A thermocouple is used in older systems with pilot lights, while flame sensors are used in newer furnaces with electronic ignition.