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

Updated on February 17, 2014
Cre8tor profile image

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

Furnace Ignition

Hot Surface Ignitor Photo
Hot Surface Ignitor Photo | Source

Is Your Furnace Not Lighting?

Do you feel it getting a bit chilly in here? Do you hear the furnace running but you're getting only cold air and it keeps turning on and off? 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 and 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 with 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 being discussed here in this hub.


There are many different types of hot surface ignitor but they all serve the same purpose.

Click thumbnail to view full-size
Here is what the hot surface ignitor looks like in place, in the furnace. Pretty tucked away and right in front of where the gas first comes into the furnace to be lit.Here is the full view of the hot surface ignitor...at least one type.Here is another type of hot surface ignitor.Here is yet another type of hot surface ignitor with it's own heat sensor built in with it.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 what the hot surface ignitor looks like in place, in the furnace. Pretty tucked away and right in front of where the gas first comes into the furnace to be lit.
Here is what the hot surface ignitor looks like in place, in the furnace. Pretty 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 hot surface ignitor...at least one type.
Here is the full view of the hot surface ignitor...at least one type. | Source
Here is another type of hot surface ignitor.
Here is another type of hot surface ignitor. | Source
Here is yet another type of hot surface ignitor with it's own heat sensor built in with it.
Here is yet another type of hot surface ignitor with it's own heat sensor built in with it.
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.

What is a Hot Surface Ignitor?

The hot surface ignitor is a device that is 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 the respect that it's 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 how fragile this component can be. 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.


I Think I Can. I Think I Can.

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

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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 and didn't, it may be in a lockout phase. This is a safety default of your furnace and can be over-ridden 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 it's thing, you'll here 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 often.


Click thumbnail to view full-size
Here is an example of the electrical connection of your hot surface ignitor. Unplug one and plug in the other...it's that easy.Here is a side view of the ignitor in place. See the bracket leading to the right? The tip of that screw there is the only screw I need to remove.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.
Here is an example of the electrical connection of your hot surface ignitor. Unplug one and plug in the other...it's that easy.
Here is an example of the electrical connection of your hot surface ignitor. Unplug one and plug in the other...it's that easy. | Source
Here is a side view of the ignitor in place. See the bracket leading to the right? The tip of that screw there is the only screw I need to remove.
Here is a side view of the ignitor in place. See the bracket leading to the right? The tip of that screw there is the only screw I 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

Replacing a Furnace Ignitor | Hot Surface

Replacing the hot surface ignitor is really very easy. The key again is to be careful because of how fragile these can be. I actually recommend, and did when I worked on furnaces full time, buy 2 whenever I went to replace one. This saved me a trip more than once and when doing my own, I ended up with a spare that I know I'll use someday. These tend to go out about every 5 or 6 years and you never know when that will be so it's good to have one on hand.

Another important aspect of this 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 brand or sister brand of your unit and have the model number of your furnace ready. Take the old part with you along with it's mounting bracket and electrical connector. Sometimes the only difference in the ignitors will be these 2 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.

As for the actual replacement...I don't mean to dumb it down but you take out a screw, remove the part and undo the clip. That's it. It goes back just the way it came out, only more carefully.


Furnace Repair Tips

If you see the ignitor is working like it seems 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 at all going on 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 or if not, will someday when you need this type of information.

As always, my aim is to help you and my hope is 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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    • profile image

      Scott 5 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 7 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 7 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 4 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 4 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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