How to Tell if Flame Sensor Is Bad: 6 Signs You Shouldn't Ignore

Professional Services
November 15, 2023

In a Southeastern Wisconsin winter, your heating unit is your home's best friend. Your furnace creates a warm, comfortable environment in which you and your family can relax and stay healthy. Without it, you'd all be piling on sweaters and shivering while indoors, not to mention the health risks of the severe cold.


If you're looking for "24/7 furnace repair near me" in Wisconsin, consider your search over. Professional Services offers heating unit repairs, tune-ups, and new furnace installations on gas furnaces, electric units, and more. Below, these local professionals share more about how to tell if a flame sensor is bad, which is a common issue your furnace may face in winter.


What Is the Flame Sensor and Why Is It Important?


Flame sensors are safety mechanisms within your furnace. The flame sensor does exactly what you'd expect from its name: it detects the presence of a flame. So, when the flame sensor doesn't sense a flame, the unit's pilot light remains unlit, and the gas valve closes.


When it is working correctly, the flame sensor prevents safety hazards like carbon monoxide leaks and house fires. However, a damaged or dirty flame sensor puts your home at risk because it causes the unit to constantly cycle, which may mean it overheats. The constant cycling can also create gas leaks by failing to initiate the gas valve closing or straining the components to cause cracks.


How To Tell If a Flame Sensor Is Bad


Now that you understand what it does, do you know how to tell if a flame sensor is bad? The following are six signs that you've got a faulty flame sensor on your hands:


#1 Your Utility Bills Are Higher

One of the first signs of furnace malfunction is a rise in your utility bills. A blocked or broken flame sensor causes the unit to strain more as it heats your home. This straining can cause short cycling that drives up your energy costs.


#2 The Unit Is Outdated

Even the best heating units are not built to last forever. On average, furnaces last about 15 to 20 years when well-maintained. If your furnace is older, it's reasonable that it may have a bad flame sensor and other components that need a replacement.


#3 You're Constantly Adjusting the Thermostat

Another sign of a bad flame sensor is the need to constantly change the thermostat settings. Are you finding it impossible to reach a comfortable temperature in your home? A bad flame sensor leads to inconsistent heat from your furnace, necessitating ongoing trips to the thermostat.


#4 The Burner Flames Are Yellow, Not Blue

If you suspect flame sensor issues, take a look at the burner flames within your unit. Yellow burner flames indicate poor furnace function. These flames turn yellow when carbon monoxide isn't venting from the furnace, which can happen with a bad flame sensor.


#5 You Notice Odd Smells

Smelling gas or an exhaust smell in your home is never a good sign. In fact, it often indicates a serious heating issue that requires immediate resolution. If you smell gas in your home, switch off the heat and call for immediate repairs.


#6 There Are Rusted Flue Lines

Your furnace's flue system guides CO gas out of your home, keeping your house and family safe. With a bad flame sensor, the flue system doesn't run properly, and the flue lines rust. This is dangerous and needs immediate professional repair services.


Check Your Flame Sensor


If you suspect issues with your flame sensor, you can do a little troubleshooting before calling an HVAC technician. Follow these steps to see if something is wrong with your heating unit's flame sensor:


  1. Turn off the power and the gas valve.
  2. Remove the compartment's mounting screw.
  3. Carefully remove the flame sensor from the unit.
  4. Clean any debris or ash buildup from the sensor.
  5. Assess it for any cracks or signs of damage.


If you find a broken or damaged furnace flame sensor, a skilled HVAC contractor must replace the sensor to ensure a safe and proper installation.


Replacing Your Flame Sensor With Professional Services


Now that you know how to tell if a flame sensor is bad, you can check your heating unit at any time. If you discover damage, seek help from a trusted local HVAC team like Professional Services. 


Whether your generator won't start or you have a faulty flame sensor, you can count on Professional Services to help. Schedule an appointment by calling 262-218-2636 today or request a service online!

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