How to Trick a Flame Sensor?

Still having problems with your furnace going on? Then read on since we know what can help you!

Written by Camilla Moln. Updated on How to Trick a Flame Sensor

Did you have this issue when you noticed that the flame on your furnace stops burning suddenly? And if it keeps on happening again and again, you might get really irritated! But how do you fix your boiler’s flame sensor if it has any issues like that?

And how to bypass the flame sensor on your furnace?

No worries and no fuss! Today we are going to share a lot of useful information with you on this topic.

From the article below, you will learn about how to bypass that flame sensor on your furnace first of all. However, this is just the beginning!

Then, we will share a few more handy facts regarding this appliance with you.

For example, you will learn how to test your furnace to see how well it is working. Also, we will explain what you should do in order to check whether your flame sensor on the furnace is not working properly.

In addition, we are going to teach you how to clean your flame sensor, and even how to replace it!

Surely, with all this in mind, fixing any issues that may happen to this appliance will never become a problem for you starting from today!

Related: How to Bypass a Flame Sensor On Your Furnace?

How to Bypass a Flame Sensor On Your Furnace?

So, you have already spotted the problem: your furnace’s flame sensor is not working properly. It turns off regularly leaving you in a cold house.

However, don’t rush and make quick conclusions since the source of this problem may not be where you expect to find it.

See, when there is no flame in your furnace, and especially when it keeps going off, the problem is most likely in the flame sensor. To be precise, the problem is that the sensor is not working properly.

When your furnace or heater won’t ignite, you should know that, in the majority of cases, 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 will not save you from trouble.

Moreover, it is not recommended to try and bypass the flame sensor on your furnace!

When people find out that they have problems with their furnace flame sensor, they usually try to bypass it. And what do they do?

They grab the pliers and simply bend the flame detector to keep it closer to the flame and thus make the sensor “see” the flame! But even though such a method of fixing can really help and make the heater unit finally sense the flame, as well as turn on the main gas immediately after the repair, this is a really bad idea to do so.

See, the flame detector is a crucial component that is used for identifying a flame and stopping the gas flow in case there is no flame.

By modifying the flame detector like that, you are putting yourself at a high risk of the appliance not lighting at all and so emitting all the unlit gas right into your house! And that could be the cause of a massive explosion!

This is why we recommend you opt for a safer way of actions. You can get your furnace back to working by undergoing a few simple procedures.

And below you will find a detailed explanation of what steps to take in case you assume that you have to bypass the flame sensor on your furnace.

With this information, fixing the appliance will be much easier for you! But first of all, let’s figure out how you can define whether or not your furnace is bad at all.

How to Bypass a Flame Sensor On Your Furnace
Credits: denfotoblog, via

How to Tell If the Flame Sensor On Your Furnace Is Bad?

So, to get things done, the very first step to getting the furnace working is ensuring whether your appliance’s flame sensor has gone bad. That’s because the improperly working flame sensor is the most common reason for all such furnace problems.

And 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 you see that your furnace flame sensor matches any of these causes or even several of them, then your flame sensor is bad and needs to be either fixed or replaced. But we will talk about it later.

Now, let’s see what you can do to clean the flame sensor on your furnace. Sometimes, simple cleaning can be very helpful and fix the situation!

How to Tell If the Flame Sensor On Your Furnace Is Bad
Credits: IndyEdge, via

Related: How to Bypass a Flame Sensor On Your Furnace?

How Does a Furnace Flame Sensor Work?

If you are not much familiar with the gas furnace “anatomy”, you may wonder how in fact the fire detector works in this appliance. Of course, being informed about this is necessary for every owner of a gas furnace because this information will help you understand more clearly what to do in case your unit is having any troubles with proper operation.

So, if we are talking about a furnace flame sensor, its method of work is pretty simple: the sensor works by detecting the presence of a flame within the furnace.

How Does a Furnace Flame Sensor Work
Credits: FroggyFrogg, via

The sensor itself is short in length and it is usually made of a thin metallic rod. This rod creates a small current of electricity in order to confirm that there is fire burning within the unit.

When the gas valve opens to start the combustion process, this gas is sent from the sensor in order to detect the presence of heat that comes from the flame. When the sensor detects the flame (and if the appliance is working as it should), heating keeps on going.

However, in case the furnace flame detector does not sense the presence of the flame within ten seconds after the gas valve opens, the furnace will be shut down. This is a pre-set preventive measure that is used for avoiding any gas leaks.

Flame sensor, Flame rod, Flame RectificationFlame sensor, Flame rod, Flame Rectification

Related: How to Clean Pilot Light? Step-by Step Guide

How to Clean Your Flame Sensor On a Furnace

If you know how a flame sensor works, you can realize why bypassing it is a bad idea. In most cases, by simply cleaning the flame sensor, you will solve all your issues.

This is why try cleaning the flame sensor instead.

And only if cleaning will not work, you can head off to more serious repairs or even replacement of the appliance. Here is how to clean flame sensor easily:

  1. Turn off the breaker or the power to shut down the furnace
  2. Close the gas valve completely
  3. Now, disconnect the wire that is connected to the flame sensor
  4. Next, unscrew the flame sensor from the burner housing with a Phillips screwdriver
  5. Pull the flame sensor out of its place
  6. Now, take a coated abrasive such as emery cloth to clean the blackened rod of the flame sensor
  7. Grab a clean piece of cloth and rub the flame sensor lightly
  8. Clean the flame sensor socket using another piece of clean cloth
  9. Finally, put the flame sensor back to its position

When following these steps precisely one by one, you will easily end up with a clean flame sensor on your furnace, and most likely, the issue with its operation will be solved.

The whole cleaning process should not take you long, usually, it takes around half an hour even if you have never done this before!

How to Clean Your Flame Sensor On a Furnace
Credits: FroggyFrogg, via

How to Test a Flame Sensor?

If for any reason you find it impossible or unsuitable for you to clean the flame sensor of the furnace, there is another option you can opt for.

Just see if the furnace sensor is ok at all.

If it is bad, it will most likely not work. Luckily, making such a check is very easy:

  • Take a multimeter with microamps (µA) measuring system
  • Keep the furnace system turned on
  • Connect it to the wire that is 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 the probe from the meter
  • Attach the other lead to the terminal of the sensor
  • Turn the thermostat on
  • Examine the reading of the 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.

How to Test a Flame Sensor
Credits: GregorBister, via

What to Do to Replace Your Furnace’s Flame Sensor?

The flame sensor replacement is needed in case your sensor test (the one we have described above) showed you that the flame sensor is not operating and it is bad.

Then, if this is the case, it must be replaced instantly.

What to Do to Replace Your Furnace’s Flame Sensor
Credits: FroggyFrogg, via

And below you can check out the step by step instruction on how to do it correctly and safely:

  • Turn your gas 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 screwdriver to remove the sensor
  • Install a new flame sensor exactly where the old one was
  • Screw it to its place and install the wiring as well

Now you can finally try and turn on your furnace and see if it is working exactly as it should be. Your furnace will work just the way it should if you follow all these steps properly.

Now you know all one may need to be able to fix the flame sensor issues with your furnace quickly, safely, and effectively! Don’t make your gas appliances malfunction, and keep an eye on them so that they work as they should!

Frequently Asked Questions

⭐ What’s the lifespan of the flame sensor of the furnace?

Two or three years.

⭐ How much does it cost to replace the flame sensor?

From 100 to 250 dollars.

⭐ What causes a weak flame on furnace?

Accumulation of too much combustion gas.

Written by
Camilla is an experienced Consultant with more than 20 years of preparing professional articles for numerous online resources. She has done a tremendous job and has learned a lot during her career. Camilla will advise you on the latest trends and give amazing tips on how to decorate a house.
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Furnace Not Working - Troubleshooting the Flame SensorFurnace Not Working - Troubleshooting the Flame Sensor