4 Best Ways How To Bypass Flame Sensor On Furnace?

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A flame sensor helps improve your furnace safety as it automatically turns off the unit if it doesn’t detect any flame. It’s a thin bent metallic rod found on the furnace’s burner. But how to bypass flame sensor on furnace? 

You can do this by removing the furnace’s access cover, identifying where the flame sensor is, then disconnecting the furnace from the power source. After that, switch off the gas control valve, remove the flame sensor, and check where the problem is. 

Remember that even though you can bypass the flame sensor, it won’t be possible to light your furnace manually. You also have to put the right bypassing safety measures in place to avoid accidents. However, it’s advisable not to bypass the flame sensor. Instead, replace or clean a dirty flame sensor and have it work as usual. 

How To Bypass Flame Sensor on Furnace?

If your furnace flame sensor is not working, you need to identify where the problem is. After knowing where the issues are, that’s when you can take the right measures to have it operational. You can do that by:

  • Detach The Access Cover on The Furnace

The first thing you need to do is check on the flame sensor to help you identify where the problem lies. It’s advisable to disconnect the furnace from the power source first. Then find where the access panel is, which can be on the sides of the furnace or at the lower part near the duct. Next, using screwdrivers, loosen the screws on the cover or open the clips that attach it to the furnace. Then tilt the cover towards your direction, lift it and remove it out. 

  • Locate The Flame Sensor

After that, identify where the flame sensor is. The flame sensor is the metallic rod with brown/white or yellow porcelain around the mounting end. The porcelain helps protect the flame sensor against grounding itself on the furnace’s metallic frame. Your furnace can have a straight flame sensor, or one bent near the end at 90 or 45 degrees. While doing this, ensure the energy supply to the furnace is off for your safety’s sake. 

  • Detach The Sensor

Then turn off the control valve and remove the flame sensor by driving out the mounting screw. Carefully check if it’s dirty or spoilt. If it’s dirty, you’ll only need to clean it, and the problem will be solved. However, a damaged flame sensor (either with a crack on the porcelain or missing parts) will require you to replace it. 

  • Re-Install the Flame Sensor

Re-install the flame sensor after you’re done cleaning or replacing the damaged parts. Then switch on the socket, open the gas valve, and test if the furnace is operational. 

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How Can I Clean a Dirty Flame Sensor?

Cleaning sooty or dirty flame sensors will not eat much of your time as it’s a simple process. You can do that by:

  • Switch off the socket and gas to the furnace. 
  • Disconnect the flame sensor
  • Then clean it out with emery cloth until all the dirt comes out. To thoroughly clean the flame sensor, wrap the emery cloth around it, then gently move it up and down. After that, move the emery cloth from side to side to remove as much dirt as possible. 
  • After that, fix the flame sensor back and test if your furnace is working as usual.

You should use an emery cloth with a fine grit to avoid spoiling the soft metallic surface of the flame sensor. If it gets spoilt, it will have groves that will have carbon buildup from the burner flames. In the end, this will cause another blockage that will force you to clean the flame sensor repeatedly. 

Replacing A Spoilt Flame Sensor

If the flame sensor doesn’t work after cleaning it, you need to check if it’s spoilt. You can find out this by looking out for the damaged part visually. After you find out that the flame sensor is destroyed, you need to replace it to have it functional as before. 

Do this when replacing it:

  • First, remove the mounting screws and get out the spoilt flame sensor.
  • Disconnect the wire from the flame sensor
  • Then install the new flame sensor in the right position to avoid further complications.
  • Screw back the mounting screws
  • Finally, connect the wire to the replaced flame sensor.

How Can I Tell If My Furnace Flame Sensor Has a Problem?

One of the major signs of a bad flame sensor on a furnace is when it experiences a short cycle or lights for a few seconds then goes off. Secondly, the flame sensor can be dirty with soot or have a corroded surface. Finally, the flame sensor can also fail your furnace when its porcelain is cracked. Some of these issues you can easily solve, but others require you to work with a professional. 

Read Also: Why Your Goodman Furnace Won’t Ignite & How to Solve It

Frequently Asked Questions

Is flame sensor the same as thermocouple?

No. However, they perform the same function, which makes many people confuse it with being the same thing. For example, a flame sensor is found in furnaces with an electronic controller. But the thermocouple is part of the standing pilot furnaces with pilot lights. 

How much will it cost me to replace the flame sensor?

If you decide to replace the flame sensor yourself, it will not cost you much as you’ll only buy a new sensor. Cleaning it will also need you to buy the emery cloth only. However, if you’re working with a professional, the cost will be a bit higher and vary from place to place. The cost of the sensor will also depend on the type of furnace you’ve got. 

After how long should I replace the flame sensor on my furnace?

It’s advisable to replace the sensor after about two or three years. But this majorly depends on how you maintain it. However, when it has issues, you can replace it at any time.

Can my furnace work without a flame sensor?

If your furnace has no flame sensor, it will be a danger in waiting. This is because the furnace will be producing gas even when it shouldn’t. But if it has a flame sensor with a problem, it will automatically shut down after not detecting a flame. 

Can I bypass a flame sensor, and what happens if you do so?

Yes. You can bypass the flame sensor. However, if you do so, you can’t manually light your furnace, and you’ve got to have proper bypassing safety measures in place. But it’s advisable not to bypass the flame sensor. Instead, clean or replace it to have it operational. 

Can you test a furnace flame sensor?

An individual could test a furnace flame sensor by using a multimeter to measure the resistance of the sensor.

How long do furnace flame sensors last?

Furnace flame sensors can last anywhere from 1-5 years. They vary in length depending on the quality and the environment they’re used in.

Does a flame sensor need to be grounded?

The flame sensor does not need to be grounded, but it is best if it is grounded. The flame sensor in the smoke detector makes the alarm sound in case of a fire by detecting when there is smoke and heat from a fire in the room. If this device was not grounded, then the connection to the electrical ground would not be present for protection against electrical shock; therefore, we recommend that all smoke detectors be grounded.

Bottom Line

How to bypass flame sensors on the furnace is something you can do with ease. However, you need to be cautious as it can be dangerous. In most cases bypassing is discouraged, and experts advise cleaning or replacing a spoilt flame sensor to have it work as before. When cleaning your flame sensor, ensure you’ve got the right cloth that won’t damage this delicate part of the furnace and incur additional expenses.

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