Furnace Won't Light? How to Replace a Furnace Ignitor

Updated on January 5, 2018
Cre8tor profile image

Dan has been in the HVAC industry for 22 years with experience ranging from installation and service to sales and distribution.

Hot surface ignitor.
Hot surface ignitor. | Source

Is Your Furnace Not Lighting?

Do you feel it getting a bit chilly? Do you hear the furnace running, but you're getting only cold air and it keeps turning on and off? And then...exactly—you hear nothing.

Well, depending on what time it is, you may want to get some extra blankets, but the good news is, you might be able to figure this one out for yourself and even fix the problem pretty easily.

Diagnosing a problem with your hot surface ignitor (silicon nitride or carbide ignitor) is rather simple, and replacing it is just as easy. So strap on your work boots, get out your toolbox, and let's get this thing running. (Just kidding. You won't need work boots at all and probably only one tool.)

Furnace Safety

As always, when working with a gas and/or electric appliance, be sure that the power is off and that you take great care of your safety. Do not guess or assume anything when working on your furnace. It is up to you to decide if you are suited to perform the repair discussed in this article.

What Is a Hot Surface Ignitor?

The hot surface ignitor is a device used in most modern furnaces to ignite the gas you use for heat. It's a relatively simple component that works quite like a toaster in that its heat is generated by forcing 120 volts through an exposed, resistant material. In this case, that material is usually silicon carbide or silicon nitride.

Now, I used the word resistant lightly. Make no mistake, this component is very fragile. It is electrically resistant, not impact resistant at all. When handling this component, be very careful not to whack it against anything, and don't touch it with your bare hands. Even the slightest crack in the ignitor can cause it not to work, and the oils from your skin can cause failure too.

Various Types of Ignitors That All Serve the Same Purpose

Here is what a hot surface ignitor looks like in place in the furnace—fairly tucked away and right in front of where the gas first comes into the furnace to be lit.
Here is what a hot surface ignitor looks like in place in the furnace—fairly tucked away and right in front of where the gas first comes into the furnace to be lit. | Source
Here is the full view of the ignitor shown above. This is one of a few types.
Here is the full view of the ignitor shown above. This is one of a few types. | Source
Here is another type of hot surface ignitor.
Here is another type of hot surface ignitor. | Source
Here is yet another type, with it's own heat sensor built in.
Here is yet another type, with it's own heat sensor built in.
Here is a spark ignitor. This uses an electric spark to light your gas furnace. I just thought it'd be good to show the difference.
Here is a spark ignitor. This uses an electric spark to light your gas furnace. I just thought it'd be good to show the difference.

Diagnosing the Problem

Diagnosing a faulty hot surface ignitor is really quite simple. There are very few times where your eyes and ears will fool you, so odds are, if you watch and listen, you'll know if your ignitor is bad.

Simply watch the furnace the next time it tries to start up. There is a chance that if your furnace was trying to start but didn't, it may be in a lockout phase. This is a safety default on your furnace and can be overridden by shutting off the main power to the unit, waiting approximately 60 seconds, and then turning it back on again. Now your furnace should try to restart, so watch and listen.

As the furnace begins to do its thing, you'll hear the fan come on. Then, perhaps—if you have one—you'll hear the smaller inducer fan turn on. Shortly thereafter, you should see your hot surface ignitor begin to glow followed by a "tick" sound. This "tick" is the gas valve opening. Finally, you should see the flames ignite.

No glowing? No fire? Your hot surface ignitor is bad. At least that will be the case most of the time.

I Think I Can. I Think I Can.

Is your furnace lighting and shutting off, then lighting then shutting off?

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Here is an example of the electrical connection of the ignitor. Unplug the old one, and plug in the new. It's that easy.
Here is an example of the electrical connection of the ignitor. Unplug the old one, and plug in the new. It's that easy. | Source

Replacing a Furnace Ignitor

Replacing the hot surface ignitor is simple. The key, again, is to be careful because of how fragile these can be. I don't mean to dumb it down, but you just take out a screw, remove the part, and undo the clip. That's it. The new part goes back in the same way the old part came out, only more carefully.

I do recommend buying two; I did this when I worked on furnaces full time. This saved me a trip more than once, and when repairing my own, I ended up with a spare that I know I'll use someday. These tend to go out about every five or six years, and you never know if it might be sooner, so it's good to have one on hand.

Another important point is being sure you get the proper replacement. You won't find these at your big-box home improvement stores, so call a local wholesaler for a replacement. Be sure to call one that deals in your unit's brand or sister brand, and have the model number ready. Take the old part with you along with its mounting bracket and electrical connector. Sometimes, the only difference in the ignitors will be these two items, but they are an important difference, so you want them to be correct, too. You can expect this part to cost somewhere between $25 and $50—still much cheaper than a service call.

A side view of the ignitor in place. See the bracket leading to the right? The tip of that screw is the only screw you need to remove.
A side view of the ignitor in place. See the bracket leading to the right? The tip of that screw is the only screw you need to remove. | Source
And here is a view of the burner assembly. To the right you see the wiring and clip leading to the ignitor and on the left, the wire leading to the flame sensor.
And here is a view of the burner assembly. To the right you see the wiring and clip leading to the ignitor and on the left, the wire leading to the flame sensor. | Source

Furnace Repair Tips

If you see the ignitor is working like it should, then you likely have a different problem. Try checking a couple of these items for other easy fixes.

  • Fuse: There is a 3-amp fuse on your circuit board. Of course, if it blows, then you likely don't have anything going on at all in the furnace.
  • Flame Sensor: This is a very common problem with furnaces and, again, another easy fix. With this, your furnace will likely fire and then shut down almost as fast.
  • Thermostat: Perhaps it's time to replace your old thermostat with a newer, more accurate one. Not that your furnace shutting down has to do with accuracy, but an aged thermostat can cause a furnace to do funny things, too.

I hope that something here has the home-fires burning again.

As always, my aim is to help you, and my hope is that you'll help others.

What do you think?

Do you think this is a project you can handle if need be?

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Comments

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    • Cre8tor profile image
      Author

      Dan Robbins 2 months ago from Ohio

      Be sure the igniter you're using is the proper voltage...typically 120V or 80V and also that the power being supplied by the board is proper. If not, it could be causing the problem.

    • profile image

      Richard M Cortellini 2 months ago

      since replacing the last ignitor 2.5 years ago, I've replace the ignitor 2x in the last 2 weeks.

    • Cre8tor profile image
      Author

      Dan Robbins 4 months ago from Ohio

      kalifornia - I'm leaning towards the high limit/fan switch or one of the roll out switches. It's sure acting like a flame sensor but with that ruled out these would be my suspects. They are rather inexpensive parts. I hope it is as those are easy fixes but still hard for me to be sure from here. The video was very helpful though there is no real way to be sure without running electrical tests which it sounds like you're capable of doing so try testing those components. Best of luck and Happy New Year!

    • profile image

      kailfornia 4 months ago

      furnace (rheem criterionII ~ 1999) shuts off after 7 seconds.

      1. replaced control board

      2. replaced flame sensor and checked with microamps / its working.

      3. checked connections, all seem good.

      stumped on where to go for troubleshooting from this point.

      video of issue here:

      https://youtu.be/KLWK2VCf0ak

      any help very appreciated. thanks!

    • profile image

      Scott 15 months ago

      My igniter went out.

      Checked it and had a small break in It.

      Took a very thin piece of copper sheathing I had left over from trimming wood joist outside.

      Gently wedged it in crack on ignitor.

      Turned on furnace and the copper actually vaporized into a carbon like sunstance.

      Wah lah

      Ignitor lit and has worked for days.

      Long enough for me to get a replacement.

    • Cre8tor profile image
      Author

      Dan Robbins 17 months ago from Ohio

      It sounds as if it's maybe a pressure switch which would be the cheapest easiest place to start.

    • profile image

      George Wetherby 17 months ago

      I have a Tran XE78 gas hot air furnace. The unit runs almost a full cycle but the flame turns off the inducer slows down , then it speeds up, the flame turns on again and the cycle continues for approx. 3-5 minutes then turns off? Any ideas?

    • Cre8tor profile image
      Author

      Dan Robbins 5 years ago from Ohio

      Thank you kindly vespawoolf. I realize how exciting HVAC is to read about so I do try to sprinkle it with a bit of humor to help ease the pain. LOL! I do hope that should you ever need it, this will come in handy.

    • vespawoolf profile image

      vespawoolf 5 years ago from Peru, South America

      Normally I wouldn't read a hub about repairing a furnace, but your writing made it enjoyable! I'm sure this is very helpful information for a DIYer with a broken furnace. Voted up!

    • Marcy Goodfleisch profile image

      Marcy Goodfleisch 5 years ago from Planet Earth

      I'm afraid I had to vote 'no' on this one - I think my safety and the safety of maybe my entire neighborhood might hinge on that choice. I didn't know this part of the furnace existed! As always, I learn so much from your hubs! Voted up and up!

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