How Often Should A Flame Sensor Be Replaced?

Ryan Womeldorf
by Ryan Womeldorf

Furnaces are integral to the overall comfort of a home. During even the coldest of winter months, we can remain nice and warm thanks to our furnace. But the furnace has a lot of components to it that can break or need replacing, such as the flame sensor unit, for instance.

Generally speaking, the flame sensor should be replaced every two to three years as preventative maintenance. Some technicians also recommend changing it any time that there is a flame current issue.

In this article, we will talk more about the flame sensor and how often you should replace it so that you can keep your furnace running in tip top shape throughout the winter. In addition, we provide you with ways to tell whether your flame sensor is bad and what you can do about it.

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What Is A Flame Sensor?

A flame sensor is a built-in safety feature in gas heating equipment. When the furnace goes through the ignition sequence, there is a process where either a hot surface igniter or a spark will be the one to light the gas.

The flame sensor will create a current of electricity that gets quantified in what are known as micro amps. The furnace’s control board will look for the proper level of micro amps; if it doesn’t find them, the furnace will cut off fuel to prevent potential explosions.

But the flame sensor can wear down over time, especially if it isn’t cleaned. There can be a build up of carbon or oxidation that can keep the flame sensor from working properly and ultimately lead to a malfunction.

Good Flame Sensor vs Bad Flame Sensor

When the flame sensor is properly working, it will act to shut down the gas valve when it doesn’t sense a flame at the moment the furnace should be firing. The flame sensor is a safety valve and is an integral part of the furnace.

A bad flame sense won’t be able to sense the heat and, thus, will not shut down the furnace. When this happens, the furnace can fire up and be burning hot without the sensor knowing that it is taking place. This is extremely dangerous.

Why And When To Replace The Flame Sensor

Even if the flame sensor has been working optimally, it is a good idea to replace it as preventative maintenance every two or three years. This will ensure that the sensor remains working functionally and avoids potential issues.

When the flame sensor is dirty or malfunctioning, it can have two impacts. The first is that it may prevent the furnace from lighting because the microamp levels can’t be quantified. The second is that it may come back with an improper reading and ultimately lead to an explosion.

Safety is paramount with your furnace, so it is always better to be safe than sorry and simply replace the flame sensor if it is acting up.

Diagnosing Potential Issues

If you think that there may be an issue with your flame sensor, the first thing to do is turn off the electrical power to the furnace. You can do this at the furnace itself or at your electrical box, whichever you feel.

Close off the gas valve and then take the flame sensor mounting screw out. When this step has been completed, you can gently pull out the flame sensor and take a look at it. If it looks like the unit is in pretty good shape but a little burnt or dark, it can just need a simple cleaning.

If you do notice a crack or missing piece in the porcelain insulation, you will need to replace the sensor entirely. After replacing or cleaning, remount the flame sensor before turning the power back on, opening the gas, and lighting the furnace.

Cleaning The Flame Sensor

If you feel that the flame sensor is still in working condition, it is a good idea to keep it clean. This is to keep any corrosion or dirt from deteriorating the metal surface. This will ensure that the flame sensor stays in working condition for longer.

When cleaning a flame sensor, use a fine grit emery cloth; the finer the grit the better. Using a fine grit is meant to avoid the grooves that the flame sensor’s soft metal has. Too coarse of cloth can damage those grooves.

The grooves of the flame sensor can collect carbon when the flames of the burner are ignited. As the carbon begins to build up, the sensor will begin to fail, and it will require cleaning.

Replacing The Flame Sensor

Remember, the process begins by taking out the mounting screw so that the flame sensor can be removed. Carefully detach the flame sensor before attempting to replace or clean it. You will be able to tell if the sensor is broken because it will show visible damage and cleaning will not change the issue.

You can find a flame sensor and just about any local furnace supply store or even big box hardware stores. If that fails, check out an online seller. This way, you can get the exact sensor that you need for your unit.

What Does It Cost To Replace A Flame Sensor?

This depends on whether you plan to do the replacement yourself or call in a repair service. If you don’t feel comfortable taking on the task yourself, calling in a repair service will run anywhere from $80 to $250 depending on the service that you choose.

You can save yourself on labor costs; the part will cost $30-$40 depending on what type you get and where you get it from. Keep in mind that if you are inexperienced, the money saved on repairs and wind up costing you a lot more if you perform the installation wrong.

What Happens If It Still Doesn’t Work?

If you have tried to clean or replace the flame sensor and the furnace does not work, the next step should be to call a professional. They have the experience to diagnose any other problems that may be taking place in the furnace and provide a remedy.

The only instance where one should continue to pursue a do-it-yourself fix is if they have the requisite experience. The last thing you want to do is exacerbate the problem and wind up with a much bigger mess.

Can You Replace The Flame Sensor Yourself Or Do You Need To Hire Someone?

Replacing the flame sensor on your furnace is possible to don your own, and it’s a pretty simple task. However, you need to ensure you do it properly otherwise your furnace will not function in the way that it is supposed to. Although, as with any job, if you’re not comfortable doing this on your own, it’s a good idea to call a friend who can help you. Or, you can always hire a professional.

Cost To Hire A Professional

You will spend between $130 and $470 hiring a professional to fix or replace your flame sensor. The cost, of course, depends on who you hire as well as the type of furnace you have. If you have an older furnace with parts that are harder to find then you may want to think about upgrading your furnace as a whole anyway. Always ask the contractor how much they charge, and what is included in the price so you have a good idea of what to expect.

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Wrapping It Up

Flame sensors are notorious for going bad when it comes to furnaces, which is why it is important to know how often you should be replacing them. Most sensors should be replaced every two to three years. By providing the proper maintenance and taking the right steps in caring for your furnace, you can prevent further issues later on down the line.

Ryan Womeldorf
Ryan Womeldorf

Ryan Womeldorf has more than a decade of experience writing. He loves to blog about construction, plumbing, and other home topics. Ryan also loves hockey and a lifelong Buffalo sports fan.

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