How to Tell if Flame Sensor Is Bad

Are your furnace’s flames flickering on and off in an unpredictable cycle? If so, you may have a faulty flame sensor. As one of the most important safety features of a gas-fueled heating system, it is essential to know when to replace the flame sensor since it senses the presence of flames. 

How to Tell if Flame Sensor Is Bad

In this blog post, we’ll provide basic information about how to tell if flame sensor is bad for issues with your flame sensor as well as tips on when and how to replace it. Whether you have limited DIY knowledge or no HVAC experience at all, we’ll help make sure that you stay safe from any kind of fuel-related hazards!

What Happens When a Flame Sensor Is Bad?

When a flame sensor is bad, the furnace will not be able to detect the presence of a flame and will fail to activate the heating cycle. This can cause several issues, such as reduced efficiency, an increase in energy consumption, and even safety concerns. In some cases, it may also prevent your furnace from starting up or functioning at all.

If your furnace is not starting up or functioning properly, it may be due to a faulty flame sensor. This can be difficult to diagnose since it is not always obvious when the flame sensor is bad. As such, it is important to be aware of the signs and symptoms that may indicate an issue with the flame sensor.

Contact a Professional Hvac Technician

Common signs of a faulty flame sensor include frequent cycling on and off of your furnace, inconsistent temperature readings, short or prolonged heating cycles, and unusual odors coming from the furnace. Additionally, it is important to keep an eye out for any visible soot or rust around your furnace, as these may be additional indicators of a faulty flame sensor.

If you believe that your furnace may have a bad flame sensor, it’s best to contact a professional HVAC technician to diagnose and repair the issue. Trying to diagnose and fix the problem on your own can be dangerous and may end up costing you more in the long run. An HVAC technician will be able to quickly identify if there is an issue with the flame sensor and provide a repair that is both safe and effective.

10 Methods on How to Tell if Flame Sensor Is Bad

1. Check the Wiring

The first thing you’ll want to do is check the wiring of the flame sensor. Make sure that all of the connections are tight and there are no signs of damage. If the wiring looks damaged, it’s likely that the flame sensor is bad and will need to be replaced.

Although, if the wiring looks to be in good condition, you can move on to the next step. Try to clean the connections, too, since dirt or dust can be enough to prevent it from working properly.

2. Check for Dirt or Debris

Another common cause of a bad flame sensor is dirt or debris build-up on the sensor. Over time, dust and other particles can accumulate on the sensor, preventing it from working properly. You’ll want to clean the sensor with a soft cloth to remove any dirt or debris.

Additionally, be sure to check for any corrosion or rust that may have formed on the sensor. If you find any signs of damage, replace the flame sensor immediately. Try to avoid using water or harsh chemicals on the flame sensor, as this can damage it.

3. Check for Corrosion

Corrosion is another common issue that can cause a flame sensor to fail. If you notice any corrosion on the sensor, it’s likely that it’s bad and will need to be replaced. Corrosion can occur due to humidity or other environmental factors, so it’s important to regularly check for corrosion.

Corrosion Can Occur Due to Humidity

If you do notice corrosion on the flame sensor, you’ll need to replace the entire unit. Be sure to follow the manufacturer’s instructions when replacing the flame sensor, as improper installation or wiring could lead to further damage.

4. Check for Cracks or Damage

If you notice any cracks or damage on the flame sensor, it’s likely that it’s bad and will need to be replaced. Even a small crack can prevent the sensor from working properly. Examine the sensor carefully and make sure there are no visible signs of damage.

If you find any, it’s best to replace the flame sensor right away. While it may still work with a crack, it’s best to avoid any potential problems and replace the part. Try to avoid handling the sensor too much, as oils from your hands can transfer to the part and cause it to malfunction.

5. Try Replacing the Batteries

In some cases, a bad flame sensor may simply be due to dead batteries. Try replacing the batteries in your smoke detector and see if that solves the problem. If not, the flame sensor may be the culprit. Although this is not always the case, it’s a good place to start before replacing any parts.

While you’re at it, make sure you check the connections between the batteries and the flame sensor to ensure that everything is properly connected. If all else fails, it may be time to replace the flame sensor itself.

6. Try Resetting the Smoke Detector

If your smoke detector is still not working after replacing the batteries, try resetting it. To do this, simply press and hold the test button for 15 seconds. This should reset the smoke detector and hopefully fix the problem. If the detector still does not function properly, you may need to replace the flame sensor.

 Check the Manufacturer’s Instructions

Be sure to check the manufacturer’s instructions before attempting to replace any parts. Replacing the flame sensor is a relatively simple task and should only take a few minutes. However, it’s important to take the necessary safety precautions when dealing with electricity.

Be sure to unplug the power source before attempting any repairs. Lastly, make sure you have the correct replacement parts before beginning any repairs. If you have any doubts, contact a qualified professional to assist you in replacing the flame sensor.

7. Try Cleaning the Contacts

If your smoke detector still isn’t working after resetting it, try cleaning the contacts with a cotton swab dipped in rubbing alcohol. This will remove any dirt or debris that may be preventing the contacts from making a good connection. If the contacts are visibly corroded or broken, you will need to replace the flame sensor.

Cleaning should be done regularly, as it can help to avoid this problem in the future. However, if you have an old sensor, it may be time to replace it. While a new sensor will cost you more initially, it should last longer and be less likely to malfunction. This can save you money in the long run from having to frequently replace malfunctioning sensors.

8. Try Moving the Detector Closer to the Source of the Flames

In some cases, a bad flame sensor may simply be due to its location. If your detector is too far away from the source of flames, it may not be able to detect them properly. Try moving your detector closer to see if that solves the problem. If not, then you may have a faulty detector and will need to replace it.

Due to Its Location

9. Try Replacing the Entire Smoke Detector

If none of these solutions work, it’s likely that your smoke detector is simply old and needs to be replaced entirely. Smoke detectors only have a lifespan of about ten years, so if yours is older than that, it’s probably time for a new one anyway.

Your best bet is to purchase a new smoke detector that uses the same type of flame sensor as your old one. This way, you can be sure that the new one is compatible with your current system. After replacing it, make sure to test its sensitivity levels and replace any old batteries as needed.

10. Call an Expert

If none of these solutions work, it’s best to call a professional for help. A professional can diagnose the issue and provide the best solution possible. They’ll be able to tell you if your flame sensor is bad and will be able to replace it if need be.

If you’re having trouble with your furnace, don’t hesitate to take this step. It’s always best to be safe than sorry when it comes to heating systems. A professional will be able to keep you warm in the winter and help keep your home running smoothly for years to come. So don’t wait any longer–call an expert now!


If your furnace is having trouble igniting, it might be time to check the flame sensor. While this might sound like a daunting task, it’s actually pretty simple. With a little elbow grease and some patience, you can easily figure out if your flame sensor is bad. Thanks for reading our blog post on how to tell if flame sensor is bad! We hope you found it helpful and informative.

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