How to Bypass Flame Sensor on Furnace [What Actually To Do] 

When you are looking for how to bypass flame sensor on furnace, I bet you, here you want to know how to check if the flame sensor is okay or not.


We have a few ways to tell you how to trick a flame sensor. In this article, you will get to know about it all. So keep on reading.

How to Bypass Flame Sensor on Furnace [What Actually To Do] 

If there is no flame in your furnace, 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 trick 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.

How to Know if the Flame Sensor is Bad

The first step to getting the furnace working is ensuring whether your furnace flame sensor has gone bad. Here are the most common signs of a faulty flame sensor:

  • Take a look at the flame sensor and see if it is rusty
  • The furnace will light up only to 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. 

How to Clean a Flame Sensor

If you know how does 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 flame sensor easily:

  • Turn off the breaker or the power to shut down the furnace
  • Closs the gas valve completely
  • Then disconnect the wire that is connected to flame sensor
  • Then unscrew the flame sensor from the burner housing with a Phillips screwdriver
  • Pull the flame sensor out of its place
  • 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 to its position

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

How Do You Test a Flame Sensor?

If cleaning the flame sensor doesn’t work for you, then see if the flame sensor is okay. A bad sensor will surely not work. Here’s how to easily test a flame sensor:

  • Take a multimeter with microamps (µA) measuring system
  • Keep the furnace system turned on
  • Connect it to the wire leading to the gas valve 
  • Connect the other side of the multimeter to the sensor terminal
  • Take the lead away from the flame sensor
  • Connect the lead to a probe from the meter
  • Connect the other lead to the sensor terminal
  • Turn the thermostat on
  • Examine the multimeter reading

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. 

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 screw driver 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

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.


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 on 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 of a 2000 square foot home. 

Final Words: 

Knowing how to bypass 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.

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