how to tell furnace ignitor went bad

How to Check If Furnace Ignitor Is Bad

Furnaces are complicated and tricky to address devices. They come with features that provide accurate and reliable performance for a fair amount of time, but they take a lot of wear, so the problem’s risk is never null.

One of the components that affect the furnace’s proper functioning right away (you won’t be able to miss it, that is) is the ignitor. Many things can go wrong with your furnace, and an ignitor going bad is probably one of the problems you “want” to have. It’s cheap and easy to deal with a bad ignitor.

How to tell if the furnace ignitor is not working right?

You will turn the furnace on and realize that there is no heat. Diagnosing a lousy ignitor is relatively straightforward, and most homeowners will be able to do it.

  • Ensure that the thermostat setting is above the temperature inside the house. Set the thermostat to 70f degrees if the temperature inside is 65f degrees.
  • After you turn the furnace on, you should be able to hear the motor start in the furnace (it’s the inducer motor). It will make the airflow moving through the combustion chamber and outside through the chimney. It creates a vacuum so that the dangerous exhaust fumes with carbon monoxide are correctly vented.

Should none of these steps happen, it means that the thermostat is terrible (it’s very cheap to repair or replace). If it’s not the thermostat, a lousy inducer motor (it’s moderate to pricey), a damaged control board (expensive), or a bad pressure switch (it’s supposed to detect when the vacuum was created or not for safe venting).

Don’t panic and don’t call the HVAC technician just yet; you still need to check a couple of things:

The circuit breaker

It’s labeled on the electrical panel. It’s in the middle position when it’s tripped, so you will have to turn it off and then back on for resetting it. When the furnace starts again but the circuit breaker trips also, you have an electrical problem.

The on/off switch of the furnace

Maybe someone turned off the furnace. It’s possible that someone replaced the filter, for example, and forgot to turn the furnace back on.

The chimney vent

If you can go safely up the roof, you should check if there’s snow/ice/bird nest blocking the vent. When the vent is blocked, the vacuum cannot be generated anymore, so that the pressure switch will turn off the furnace.

Inducer motor

The draft motor may run for a couple of minutes but shut off without even making the furnace fire.

When your furnace is running, and the draft vacuum is created, the ignitor will be energized. The gas valve will open, the gas will go up into the burner ports. With proper functioning, the gas will touch the hot surface ignitor, so your furnace fires up.

Should all of this happen and the furnace quits before heating the house, the ignitor is not the cause for cold air in your home.

Taking a thorough look at the ignitor

When you took all the steps above (thermostat, motor on, motor off) and you still haven’t been able to solve the problem, the ignitor could be the culprit for the furnace’s improper functioning. If you have a multimeter (it’s $30 in the hardware store), it will be relatively straightforward to check the igniter.

When you’re working on your furnace, you have to be extremely meticulous, so follow the recommended steps exactly:

Step 1

Begin with turning off the furnace at the electrical switch placed on its side. The button looks like a regular light switch. You also have to remove the top furnace panel.

Step 2

Identify the ignitor; typically is in the upper right. It features a white base with a black part going into the furnace port. Ignitors also come with wires for energy.

Step 3

Once you’ve spotted the ignitor, you will also have to remove the screw/screws that keep it in place. Pull it out and disconnect it from its wiring.

You’re supposed to hold the ignitor, as the plug is still connected to the furnace. Make sure not to touch the igniter stick, but only the base. It’s because of the oil from your skin that may get to the ignitor; should the ignitor isn’t bad and you put it back in place, the oil will burn, generate a hotspot on the ignitor and break it.

Step 4

Take a look at the ignitor. If you notice any cracks, you should replace it with a new one. Keep in mind that damages could be complicated to spot, so further steps are necessary.

Step 5

You need to see if the ignitor receives any power or not. You will have to turn the power switch on so that the inducer motor begins.

Step 6

Carefully put the meter leads into the plug inside the unit, one in every hole. Ensure that you don’t stick the leads very far into the plug; you don’t want to spread out and break the connectors. Take a look at the meter. When it displays +/-120 volts, the igniter receives power, but it’s terrible.

Step 7

You also have to check the ignitor’s resistance. It’s time to turn the meter to the ohm settings, utilizing the meter leads and touching one to every side of the ignitor plug (it has to be disconnected from the wiring). When electricity runs through the ignitor, it means that it’s okay, and it should read from 40 to 200+ohms.

When there are only a couple of ohms, the ignitor is bad.  If the reading is high above +200ohms, the ignitors are wearing out, so replacement isn’t a bad idea.

What do you do if the ignitor isn’t bad?

Should the ignitor be useful, there’s something else going on with the furnace, and you should call the HVAC technician. However, when he comes, make him replace the ignitor either way, especially if your furnace is more than seven years old.

Typically, you will pay from $30 to $50 for replacing the ignitor, but you won’t have to deal with cold air in the middle of the winter (not because of the ignitor, anyway).

As always, you may replace the ignitor on your own, and it will cost you only $15 to do it. With the professional service, expect to pay anything between $75 to $200. The ignitor is priced from $15 to $60, and the replacement won’t take longer than 10 minutes. Most HVAC companies will charge a minimum service fee of $75 just for showing up. Obviously, you will pay a lot more when you call them at night or the weekends.


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