Furnace Won't Light? How to Replace a Furnace Ignitor
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.)
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
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.
Check the Sensor
- How to Clean a Furnace Flame Sensor
What is a flame sensor? What does a flame sensor do? How can I clean a flame sensor? It's all here. A dirty flame sensor is a common cause of furnace problems. This simple furnace repair tip could save you $100-$150.
I Think I Can. I Think I Can.
Is your furnace lighting and shutting off, then lighting then shutting off?
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.
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?
Need More Furnace Help?
- How to Figure Out What is Wrong With Your Furnace
Do you know how your furnace is supposed to work? If not, how do you intend to fix it? This hub will help you understand the proper working order of a furnace so that you can pinpoint problems and repair them or know what to tell the people who will.
Questions & Answers
After refueling my furnace it won't kick back on. I have turned it off and on a few times trying to bleed the air out. What else can I do?
I don't believe kicking the furnace off and on to bleed is the proper way to do so. I think it's more like bleeding a broken line if you ran it empty. I would have a professional take care of this because I do know if done wrong you can cause damage to the unit and potentially a hazardous situation.
What is the correct orientation of the ignitor shield? Does it go between the ignitor gas source, or does the ignitor go between the shield and gas source?
There is no igniter shield that I am aware of outside of a grill to protect it from grease. I'm not sure what you have or are working on, but nothing should be between the igniter and gas supply. That could slow ignition, thus creating a build-up of gas before ignition and that's bad.