How To Bypass Flame Sensor On Furnace [What Actually To Do] 

In short, you can’t bypass your furnace flame sensor because it’s risky. Plus, bypassing the sensor won’t fix your furnace flame sensor issue. So, we can’t tell you how to bypass flame sensor on furnace. But, we can show you the easy ways of fixing the flame sensor and finding the sensor working fine again.

However, for your better understanding, before knowing how to trick a flame sensor and troubleshoot it, you should know what’s the flame sensor and how it works on a furnace. So keep on reading…

What Is A Furnace Flame Sensor?

A flame sensor is an essential safety component of any gas heating unit. Usually, it is assembled inside the burner. During the ignition cycle, it mainly determines whether it has to supply electricity or shut off the power. 

The complete process is done on flame detection. When the gas ignites, the flame sensor starts creating a current of electricity. Also, if there is no flame, the flame sensor turns off the heater in order to prevent any mishap. 

How Does A Flame Sensor Work?

Depending on the ignition cycle, the function of the flame sensor is done. For your information, flame sensors are a vital element of a gas heater or furnace. It works in order to provide safety during ignition when there is no flame but gas leaking. 

The flame sensor identifies the presence of the flame in the heater. If it can’t be able to find any flame, it immediately shuts off the furnace. On the contrary, the sensor generates a current of electricity when it detects the presence of the flame. If the furnace turns off by tripping the safety switch, you may have to reset the unit.

How To Bypass Flame Sensor On Furnace

When you are looking for how to bypass a flame sensor on your furnace, we bet you, here want to know how to check if the flame sensor is okay or not. Right? Listen, here we are telling you the reality.

If you find there is no flame in your furnace, then the fault may not be where you think. When furnaces don’t function properly, it is usually because your flame sensor is bad.

When your furnace or heater won’t ignite, you should know, here, most probably, a bad flame sensor can be the main culprit. A bad flame sensor won’t allow any ignition in the furnace. This is why knowing how to bypass a flame sensor won’t save you from trouble. However, you can get your furnace back to working by ensuring a perfect flame sensor. 

Below we have discussed what you actually need to do when you think you have to bypass the flame sensor on the furnace. Knowing the following things will help you fix your furnace easily.

Know If The Flame Sensor Is Bad or Not

The first step to getting the furnace working is ensuring whether your furnace flame sensor has gone bad. Here are the steps and signs to sort out a bad furnace flame sensor:

  • Unplug the furnace power plug and be sure the power to the furnace is cut off
  • Then turn off the furnace gas control valve and open the furnace access cover
  • Now, find out the furnace flame sensor and open it
  • Take a look at the flame sensor and see if it is rusty
  • If it’s rusty, the furnace will light up only and then shut off after a while.
  • See if you can notice any kind of crack on the flame sensor porcelain
  • The furnace will go into ‘Lockdown Mode.”
  • The furnace will not light up at all

If your furnace flame sensor matches any of these points, then your flame sensor is bad. 

Furnace Flame Sensor Troubleshooting

Troubleshooting your furnace flame sensor will depend on the flame sensor’s condition. If you find the sensor is rusty or dirty, then cleaning the rust or carbon build-up will be the best solution. Carefully remove the rust, dirt, and carbon build-up, and reinstall the flame sensor. And, hopefully, you will find the sensor is working.

But, if you discover the flame sensor is damaged or broken, then cleaning won’t restore the sensor. You must have to replace the flame sensor.

Safety Tips: While troubleshooting the flame sensor, make sure you have unplugged the power cord of your furnace and shut off the gas control valve.

How To Clean A Dirty Flame Sensor

If you know how a flame sensor works, you will realize why bypassing it is a bad idea. In most cases cleaning the flame sensor will solve all your issues. This is why try cleaning the flame sensor instead. Here’s how to clean the flame sensor easily:

  • Turn off the breaker or the power to shut down the furnace
cleaning the flame sensor step 1
  • Close the gas valve completely
cleaning the flame sensor step 2
  • Then disconnect the wire that is connected to the flame sensor
cleaning the flame sensor step 3
  • Then unscrew the flame sensor from the burner housing with a Phillips screwdriver
cleaning the flame sensor step 4
  • Pull the flame sensor out of its place
clean the flame sensor step 5
  • Then take a coated abrasive such as emery cloth to clean the blackened rod of the flame sensor
  • Take a clean piece of cloth and lightly rub the flame sensor
  • Clean the flame sensor socket with another piece of clean cloth
  • Put the flame sensor back in its position

If you follow these steps, you will have a perfectly clean flame sensor. It should not take more than 30 minutes. For a better understanding, you can watch the video.

How To Test A Flame Sensor

If cleaning the flame sensor doesn’t work for you, then see if the flame sensor is okay or not. A bad sensor will surely not work. However, to take the test, first, you need to have a multimeter with microamps (µA) measuring system.

Connect the multimeter to the wire leading to the gas valve. And then connect the other side of the multimeter to the sensor terminal and find out if the gas valve is getting the signal from the flame sensor. Remember for getting the reading, and don’t forget to keep the furnace system turned on. Now let’s proceed to test the flame sensor with a multimeter easily:

  • Take the lead away from the flame sensor carefully.
take the lead away from the flame sensor to test it
  • Connect the lead to a probe from the meter
connect the lead to a probe from the meter to test the flame sensor
  • Connect the other lead to the sensor terminal
connect the other lead to the sensor terminal to test the flame sensor
  • Turn the thermostat on and examine the multimeter reading
how to test a flame sensor with a multimeter

Your multimeter will show 5 µA and 10 µA if the flame sensor is good. A bad flame sensor will give a reading below this level. For better understanding, you can also watch the tutorial:

How To Replace A Flame Sensor

If the flame sensor test result tells you that you have a bad flame sensor, you need to change it immediately. Here’s how you can easily replace a flame sensor in your furnace:

  • Turn the furnace off
  • Wait for half an hour
  • Reach the flame sensor by removing the furnace access cover
  • Remove every connection and wire of the flame sensor 
  • Disconnect the flame sensor’s connection to the control box
  • Use a Phillips screwdriver to remove the flame sensor 
  • Install a new flame sensor where the old one was
  • Screw it to its place and install the wiring as well

It’s all about your furnace flame sensor replacement. Now turn on your furnace and see if it’s working just fine. Your furnace will work just the way it should if you follow all these steps properly.


Can you bend a flame sensor?

A flame sensor is a thin metallic rod that is not so durable. The flame rod may break down if you try to bend it. 

Can you cut a flame sensor?

As it is a thin rod, you can cut them. But it will be better if you do not cut it down to make it shorter. If you are replacing your

How long do furnace flame sensors last?

Flame sensors usually last around 2 to 3 years.

How much does it cost to replace a furnace flame sensor?

The overall cost of replacing a furnace flame sensor is around $100 to $250.

Can you bypass a flame rollout switch?

Though you can bypass a flame rollout switch, you should never try it. Rather, you can test the flame rollout switch. If the switch is found bad, simply replace it.

What causes a weak flame in a furnace?

Accumulation of too much combustion gas in the furnace combustion chamber can cause a weak furnace flame.

How much is a new furnace for a 2000-square-foot home?

$3,500 is the perfect budget for a furnace for a 2000-square-foot home. 

Final Words:

Knowing how to bypass the flame sensor on a furnace will only bring more trouble for you. Try out our recommendations instead. If you follow our suggestions, you are sure to get a perfectly working furnace. These methods have fixed many furnace flame sensors before. 

If you still have any questions, then let us know in the comment below without any hesitation.

About William

William is the founder of He has real life practical skills in fixing smoker & heating appliance issues. He loves to share his knowledge & helps others in fixing their appliances & saving their money. William firmly believes that anyone can repair his or her unit with the correct guidance & knowledge. See more at about us.

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