If your furnace ignitor goes bad, that’s good – at least in the sense that if your furnace is going to break down, this is a cheap and easy repair you can do yourself if so inclined.
How to Tell if Your Furnace Ignitor is Bad
It starts with no heat, of course, which can be a shock on a cold February morning. Here are the steps to diagnosing a bad furnace ignitor (sometimes spelled igniter, so we use both. Search engines, after all).
1. Thermostat: Make sure the thermostat setting is above the home’s temperature. If it’s 65F in the house, for example, set the thermostat to 70F.
2. Inducer Motor: You should hear a motor start in the furnace called the inducer motor. It’s purpose is to get airflow moving through the combustion chamber and out the chimney. This creates a vacuum, so that harmful exhaust fumes containing carbon monoxide are properly vented.
If nothing happens, you might have a bad:
- Thermostat (cheap repair)
- Inducer motor, aka a draft inducer motor (moderate to expensive)
- Pressure switch designed to sense that a vacuum has been created for safe venting (cheap to moderate)
- Control board (expensive) or other electrical issue.
The problem is knowing which it is. An HVAC technician is probably needed to diagnose it.
Before you call for furnace repair, check three things:
- The circuit breaker for the furnace. It should be labeled on your electrical panel. If it’s tripped, it will be in sort of a middle position, not on or off. Turn it all the way off and then back on to reset it. If the furnace starts but trips the breaker again, there’s an electrical problem, which should be diagnosed by a furnace technician.
- The On/Off switch on the furnace. Is it possible someone turned it off? An inquisitive child? Someone changing the filter (not necessary to turn it off to replace a filter, but some folks are the cautious type)?
- Your chimney vent: Only do this if you can safely get onto the roof to check to see if the vent is blocked by snow/ice, a bird’s nest or the nest of a squirrel or similar critter looking for a cozy place to spend the winter. If the vent is blocked, no vacuum can be created, and the pressure switch will signal that, and the furnace will turn off the draft inducer motor.
3. Inducer Motor part 2: The draft motor will run for a few minutes and then shut off without the furnace firing.
What happens in a working furnace is that once a draft vacuum is established, the ignitor (aka hot surface ignitor or furnace glow plug) is energized. The gas valve opens, and gas flows into the burner ports. The gas hits the hot surface ignitor, and whoosh, your furnace is firing up.
If all that happens and then your furnace quits before heating your home, it’s definitely not the ignitor.
Troubleshooting a Bad Igniter, Part 2: Inspecting the Igniter
If the 3 steps above (thermostat, motor on, motor off) happen, it is reasonable to suspect and inspect the ignitor. It’s easy to do if you have an electrical multimeter ($28 and up at home stores, hardware stores and online).
Here are the steps to troubleshooting an igniter:
1. Turn off the furnace at the electrical switch on the side of it. The switch looks just like a light switch. Remove the top furnace panel.
2. Locate the ignitor. It looks like this when in the furnace:
This igniter is in the upper right. It has a white base with a black “stick” extending into the furnace port. Ignitors also have wires (visible in the picture below) to energize them.
3. Remove the screw or screws holding the ignitor in place.
4. Pull out the ignitor and unplug if from the wiring harness. Now you’re holding the part – and the plug is still attached to the furnace.
Pro Tip: Only touch the base, not the igniter stick. Why? Oil from your hand will get on the ignitor. If it isn’t broken and you re-install it, that oil will burn and create a hotspot on the ignitor that will likely cause it to break.
5. If the ignitor is cracked, it is bad. If you don’t see a crack, move on to step 6. Cracks are sometimes too fine/small to see.
6. Check to see if the ignitor is getting power. Turn the power switch on, and the inducer motor should start.
7. Gently place the meter leads into the plug inside the furnace, one in each hole. Be careful not to stick the leads so far into the plug that the connectors are spread out and damaged. Check your meter. If it shows +/-120 volts, the igniter was getting power. This means the ignitor is bad.
8. Double-check this by checking the resistance on the ignitor. Turn your meter to the ohms setting. It is the Greek Omega symbol and looks like this:
Use the meter leads again, and touch one to each side of the ignitor plug (still disconnected from the wiring in the furnace). If electricity is flowing through the ignitor, meaning it is good, your meter should read somewhere between 40 and 200+ ohms. If your reader doesn’t register any ohms, or just a few, you’ve confirmed that the ignitor is bad.
If the ohms are 200 or higher, it means your ignitor might be wearing out. Think about pre-emptively replacing it (more on that later).
What if the Ignitor is OK?
It’s probably time to call a furnace repair company to determine the problem.
Pro Tip: Here’s something to consider. When the technician comes, have them replace the ignitor anyways. This is especially a good idea if the furnace is more than, pick a number, 7 years old? 10? What’s your risk tolerance?
In our opinion, this is a smart pre-emptive repair.
You should ask the technician about cost, but it will likely add $30 or $50 to your bill. It will ensure the old ignitor doesn’t break on you in the middle of cold weather. The technician coming to your home at a later date to replace the ignitor will set you back at least $75 and probably more, as we discuss next.
Or, of course, you can do it yourself. Get a new ignitor and install it or keep it by the furnace for future use. See below for where to buy a furnace ignitor.
Cost of Furnace Ignitor Replacement
The repair costs as little as $15 if you DIY.
Call a furnace company, and the bill will range from $75 to about $200. The part costs $15 to $60 and takes 10 minutes to replace, but most HVAC companies have a minimum service fee of $75 to more than $100 for coming to your home.
If the furnace fails during non-business hours and you want it fixed immediately, call a company advertising 24-hour service, and be prepared to pay as much as twice the price. If the temperature in your home drops below freezing, there’s a risk of pipes freezing and bursting, so definitely make the call no matter what time or day it is. The bill for repairing pipes and possibly dealing with water damage will make $250 to $300 for an emergency call for furnace repair look like chump change.
Where to Buy a Furnace Ignitor
You have many options. The local option is the obvious choice if your home is cooling off.
Local home improvement stores (Home Depot, Lowes, Menards) should have them. Some hardware stores will too.
Take the part with you, so you can make sure the one you buy is very similar. The package might say it is a Universal replacement part. That’ll likely work.
Online, you can buy them at:
- Home improvement store sites
- HVAC parts sites like RepairClinic.com and SearsPartsDirect.com
Amazon also has them.
These stores sell Universal hot surface ignitors. You can also search by your furnace brand – Rheem, Carrier, Heil, whatever.
Buying online is an option if the ignitor isn’t bad and you want to replace it pre-emptively or at least have on on-hand should you need it.
Pro Tip: If you get the part, and the electrical connector is different than the one on the old igniter, it can be cut off and spliced onto the new igniter. Most ignitors come with wire nuts for the spliced connection.
Need a Quick Video Tutorial?
Here’s a 4-minute overview of the information we’ve just discussed from a Canadian parts company.
Listen for your draft inducer motor to come on and then shut off without the furnace firing.
Check the furnace switch and circuit breaker.
Pull the ignitor, and check whether it is getting power or test it directly to check resistance.
If it’s bad, buy a new one and install it.
If it’s OK, call a furnace repair/heating & cooling company.
Hopefully, your furnace will fire after installing a new ignitor, and you’ll soon be warm again.