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We’ve all been there: you go into the basement to check on your furnace, only to find the furnace ignitor not glowing. What do you do now?

Your relationship with your furnace is probably one of those love-hate affairs that can have you purring in comfort one moment and pulling at your hair the next. That’s because furnaces come with plenty of responsibility as the price for the creature comfort and overall convenience they offer. If you neglect those responsibilities, you may find that your furnace becomes somewhat unpredictable. That’s why it’s important to take proper care of your heating (and cooling) systems at all times. However, some problems may occur no matter how diligent your efforts are—and in those cases, you’ll still need to know how to correct the problem. A furnace glow plug that isn’t glowing often falls into this category. You should learn why the glow plug isn’t glowing as soon as possible and take the required steps to solve the issue.

What Role Does the Furnace Glow Plug Play in Your Heating System?Furnace Glow Plug

Furnace glow plugs are a common form of ignitor found in many heating systems throughout the U.S. They are responsible for making sure that your furnace can burn the fuel it uses to produce heat and warm your building. As such, this makes the furnace glow plug essential, and your furnace will not be able to run without it. If the glow plug cannot ignite the pilot, the fuel in your furnace will merely sit there unused, no matter how hard you press the buttons on your thermostat.

Reasons Your Furnace Ignitor is Not Glowing

Several things can cause a glow plug to fail, so it pays to be aware of all of them. Here are the most common causes for a furnace ignitor not glowing, along with how you can recognize each issue and what you should do to fix them if you see them occurring:

  • Dirt has settled on the glow plug. Dirt on your glow plug can prevent it from successfully igniting the pilot, thus causing it to look as though it is not turning on. Dirt and dust are common culprits when it comes to failed furnace ignition because they can enter the interior of your furnace through neglected air filters and settle on all kinds of essential instruments and components. If enough dirt cakes the glow plug or pilot light, it will prevent it from being able to light the fuel in your furnace. However, you should not attempt to clean the ignitor by yourself because it is incredibly delicate and can easily be damaged by a rough touch. Instead, if you notice dirt covering your ignitor, make sure to call a professional for help. You might want to have your ducts cleaned while you’re at it since that’s probably where most of the dust is coming from. Make sure you change those filters once a month!


  • The gas pressure is not high enough to supply fuel to the system. Your furnace needs at least two things to start: a functioning ignitor, and a constant stream of fuel from the gas valve that the ignitor can burn to create heat. Sometimes, the problem with a glow plug has very little to do with the plug itself at all. Instead, it may simply appear to be malfunctioning because the gas valve is unable to send enough fuel into the system and the ignitor has nothing to ignite.


  • The glow plug is old and needs replacing. Despite even the most meticulous care and diligent home maintenance, nothing is made to last forever. Eventually, your glow plug may “flame out.” If this failure occurs, the only thing to do is purchase a new glow plug and replace the old one. Until you do, you will be unable to use your furnace. Fortunately, glow plugs are not expensive to purchase, with the required part typically costing under $120. Just make sure you have a licensed contractor that charges you a fair but competitive price for their labor, and you should be fine.


Care for Your Furnace Glow Plug, and It Will Care for You

While a furnace ignitor not glowing is a frustrating issue for any furnace owner, it is worth noting that your glow plugs are far less likely to fail if you take proper care of your furnace. Replacement should always be the last resort—and you should be able to put it off for many years by just keeping your system clean and well-maintained. If you have questions about how you can go about caring for your glow plug and maintaining your overall furnace system, contact your trusted HVAC contractor today.

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