Your furnace houses a complex ignition system with numerous components that ensure safe and efficient heating throughout your home. When your furnace’s flame sensor fails, it leaves your home vulnerable to a range of heating problems, from uneven temperatures to more significant safety hazards. Learn why your furnace isn’t starting or working as it should by understanding how a flame sensor works, the symptoms of a faulty sensor, and how to troubleshoot.
What is a Flame Sensor?
A flame sensor is a furnace safety component designed to detect a flame from the burner, which generates combustion, fire, and heat for your home. If the sensor fails to detect a flame, it shuts off to prevent gas from accumulating in the chamber — a situation that can lead to significant furnace damage or safety hazards. Furnaces have different types of flame sensors, but they work similarly.
In an electric furnace, a thin metal rod makes up the sensor, which creates an electrical current to confirm the presence of a flame. This process is called flame rectification — using a positive charge from the sensor’s current to attract negative ions from the flame. If it detects a flame, it’ll communicate with the control board and allow heating to proceed. If there’s little or no flame, the sensor won’t detect any negative ions, triggering its fail-safe mechanism to close the gas valve and shut off the gas supply.
Older gas furnace models with pilot lights often have a different type of sensor, called a thermocouple. The sensor relies on the pilot light to keep its tip at a certain temperature. If the light goes out and the thermocouple cools, it’ll shut off the gas valve.
Signs of a Faulty Flame Sensor
Flame sensors typically fail because of either corrosion, rust, silt buildup, wiring problems, or other damage. Flame sensors have an expected lifespan of about 5 years, compared to a furnace lifespan of 10 to 20 years, so you can expect yours to need periodic cleaning, repair, or replacement.
Since the flame sensor plays an important part in gas flow, ignition, and heating cycle initiation, a faulty sensor is associated with numerous symptoms. These may include:
- Short cycling
- Ignition failure
- Clicking sounds
- High utility bills
- Yellow burner flames
- Exhaust sells
- Rusted fuel lines
- Error codes
Troubleshooting a Flame Sensor
If you suspect a faulty flame sensor in your furnace, a visual inspection is the starting point for troubleshooting a furnace flame sensor.
Start by shutting the furnace off at the power source and letting it cool. Depending on your furnace, you may need to remove screws or bolts to remove the cover and access the burner assembly. You should find the sensor near the burner assembly — look for a brass or copper-colored metallic rod that’s between 3 and 6 inches long, mounted at a 45 or 90-degree angle, and tipped with porcelain. Refer to your owner’s manual if you’re unable to find the sensor. Look for these characteristics that indicate sensor damage or fault:
- Cracks or bends
- Corrosion or discoloration
- Silt buildup
- Loose, disconnected, or out of position
Other faulty components in your furnace may have overlapping symptoms of poor performance, so it’s important to rule out the straightforward fixes. Inspect your thermostat, making sure that it has fresh batteries and proper temperature settings. If you haven’t changed your air filter recently, check it for clogs and replace it as needed. Check that the circuit breaker hasn’t tripped and disconnected power if your furnace isn’t running at all. If you rule out these common problems, the issue likely lies with your sensor or more complex furnace ignition problems.
When to Call a Professional
If you’re unsure or uncomfortable with troubleshooting or find damage or buildup on your sensor, consult an HVAC technician. Certain circumstances necessitate professional help, such as safety concerns and persistent symptoms. An HVAC technician uses specialized diagnostic tools and techniques to inspect your furnace and identify underlying problems. DIY efforts may result in incorrect fixes that further compromise your furnace’s function and safety, often leading to more costly repairs.
Prompt action is important since the sensor is an important safety component. Besides straining your system and impeding its efficiency, ignoring a faulty flame sensor increases the risk of gas accumulation, gas leaks, and carbon monoxide poisoning. A dirty sensor may also repeatedly trigger, sometimes causing a lockout furnace system shutdown.Â
Preventative Maintenance
Preventative furnace maintenance helps keep your flame sensor and other components in good working order, minimizing strain on your system and lowering the risk of breakdowns or premature replacement.
Schedule professional maintenance annually to ensure the performance of your furnace, ideally ahead of peak heating season so that your furnace is ready when you need it. During a maintenance visit, your HVAC technician will conduct a comprehensive inspection, tune-up components as needed, and identify potential problems before they escalate.
Try these strategies for periodic maintenance:
- Change air filtersÂ
- Visually inspect your equipment
- Keep vents open and unobstructed
- Test your carbon monoxide detectors
Call Medley’s HVAC Technicians to Fix Your Flame Sensor
Knowing the signs of a faulty flame sensor enables you to troubleshoot and call a professional for flame sensor replacement or repair. Serving Carrollton and other surrounding areas, Medley is your go-to provider for furnace repair, maintenance, and more. Take advantage of transparent pricing, flexible financing, and more benefits when you rely on our HVAC team — contact us or schedule a service online.
Frequently Asked Questions
Can I clean my flame sensor myself?
Homeowners with HVAC knowledge or experience may feel comfortable cleaning the flame sensor, but it requires disconnecting the sensor, carefully cleaning it, and reinstalling it. It’s often best to leave this task to professionals since a fault with this safety feature can have significant consequences.
Why does my furnace keep shutting off after a few seconds?
If your furnace shuts down shortly after starting, a faulty flame sensor might be to blame. Problems with the thermostat, gas supply, burner, and other components may also cause your furnace to shut down repeatedly.