It’s the middle of winter on a, particularly cold day. Unfortunately, your furnace won’t turn ON. You’ve tried many times, but it just won’t light – the furnace ignitor isn’t even glowing!
What’s wrong? Let’s find out.
What’s a Furnace Ignitor and What Does it Do?
A furnace ignitor is an advanced ignition system that replaces the standing pilot found in traditional furnaces. Whereas the traditional furnace used a standing pilot that remained lit every second of every day, a modern ignitor only kicks on when you turn ON the furnace.
There are two main types of ignitors – the spark-plug ignitor and the hot surface ignitor. Spark plug ignitors produce an electrical spark when you turn ON the heater. The spark then lights the pilot light, which in turn lights the burners.
Meanwhile, hot surface ignition systems use a unique electrical conductor to heat an element that, in turn, lights the burners. So if your furnace typically glows red hot when you turn it on, you have a hot surface ignition furnace.
How Does a Hot Surface Ignition Systems Work?
Hot surface ignition systems use an “M” for fork-shaped silicon carbide or carbide nitride igniter to light gas flames. When you turn on the furnace, low-voltage, high-current electricity flows through the hot surface ignitor, heating it to an incredible 2500°F. The ignitor is usually glowing red within a few seconds.
Most furnaces allow at least five seconds for the carbide element to heat up fully. After five seconds, the primary gas valve opens to allow gas to flow through.
Remember that natural gas is combustible. Indeed, natural gas self-ignites when heated to 1163°F. Meanwhile, propane self-ignites when heated to between 920°F and 1020°F.
Now you can imagine when you expose any of these gases to temperatures up to 2500°F. It will combust instantly! From there, the furnace waits another five seconds to ensure that the pilot is safely lit and the gas is flowing appropriately.
If so, it allows gas to flow to the burners and lights the burner to heat the entire house. However, if something isn’t right with the burner, it keeps the main gas valve shut to prevent the risk of gas poisoning.
Why is My Furnace Ignitor Not Glowing?
The furnace may refuse to glow for many reasons. It’s important to know them so you can begin troubleshooting early.
1. Dirt has Settled on the Glow Plug
The igniter system on your furnace is very delicate. For this reason, dust and dust are the two most common culprits when the hot surface igniter fails. Whenever dirt or dust settles and covers the igniter, the surface may not heat up to the desired level (2500°F).
Solution: The easiest way to prevent dirt and dust issues is through regular maintenance. Regularly clean the ignitor to prevent buildup. However, we’d recommend professional cleaning and maintenance as the ignitor is very delicate.
2. Low Gas Pressure
Your furnace needs two things for the ignition system to go on without problems. First, the ignitor should be in great shape. If it’s damaged or compromised, ignition cannot happen smoothly. Similarly, though, you need a constant stream of fuel from the gas valve.
The igniter cannot work if it’s not getting enough gas from the valve.
Solution: You need to find out what’s causing low gas pressure. Is the gas valve blocked? Are the gas lines bent? Or is it a supplier issue? If you cannot pinpoint the problem, don’t hesitate to call an HVAC professional.
3. The Glow Plug needs Replacing
Unfortunately, the glow plug can become damaged beyond repair. A common reason is age. After many years of use, the glow pug can “flame out” or lose the ability to glow. Alternatively, the plug can malfunction due to short-circuiting.
Solution: The best solution here is to replace the plug. Fortunately, ignition plugs aren’t very expensive. A furnace glow plug costs around $120. Just make sure to hire a licensed professional for the installation. We don’t recommend DIY when replacing the glow plug.
How Often Do Furnace Ignitors Fail?
Furnace ignitors fail more often than you think. Indeed, furnace ignitors a shorter lifespan than most other furnace parts. According to Home Steady, the average furnace igniter lasts 4-7 years.
So, you should be prepared to replace the ignitor around every four years. Of course, the actual lifespan also depends on the quality of the part and level of maintenance. For example, in a well-maintained furnace, the ignitor can last the life of the appliance, i.e., at least fifteen years.
However, the opposite is also true. If you don’t take good care of the furnace, you may end up replacing it every 2-3 years.
How Do I Know If My Furnace Igniter is Bad?
Unfortunately, it’s not very easy to pinpoint furnace ignitor issues. That’s because the signs of furnace ignitor failure may also point to various other furnace failures. Nevertheless, you likely have an ignitor issue if you observe one or more of the following;
Furnace Blows Chilly Air
If your heater seems to run, but it gives off chilly air, you probably have a failed ignitor. The reason you’re getting chilly air is that the burner is OFF. The inducer fan may be running, creating the impression that the entire furnace is operating.
However, if the igniter is bad, the burners cannot come ON. Therefore, you can’t have heat.
Furnace Starts and Stops, Repeatedly
The repeated on-off operation is also known as short cycling. Furnaces can short cycle for many reasons. However, a bad ignitor is top of the list. A dying ignitor can rarely hold enough charge to heat the furnace and properly light the heater.
So, it may attempt to light the burners, then go off abruptly when the charge is depleted. When this happens, the furnace waits 60 seconds before attempting ignition again. This can go on repeatedly until the furnace enters “lockout.”
Furnace Stops Running Altogether
The furnace may also stop running completely if you have a bad ignitor. This isn’t a sign of a breakdown in other parts of the furnace but a built-in safety mechanism to protect the user from gas poisoning and fire risk.
If your furnace stops working because of a bad ignitor, you need to reset the furnace manually to continue using it.
Furnace Refuses to Start
Finally, it’s also apparent that a furnace with a problematic ignitor may refuse to start. This can happen for two reasons. First, the faulty ignitor may not produce the charge (or spark) to start the burner.
So, the unit will remain off until you fix the problem. Alternatively, your furnace may enter lockout after several ignition attempts, thus becoming unresponsive to inputs.
How Do You Test a Furnace Ignitor?
By physically inspecting it and using a multimeter to check whether the furnace ignitor conducts electricity. The following is a step-by-step process you can follow;
- Turn off the furnace: It’s best to turn off the furnace at the thermostat. However, you can also turn it off using the furnace’s On/Off switch.
- Turn off power and gas: In addition to turning off the furnace, you must also turn off the electric power (ideally at the breaker) and gas supply (at the gas valve).
- Remove the service panel: Unscrew or lift off the front panel to access the igniter. On standard furnaces, the ignitor is mounted on a V-shaped bracket near the gas port. It has a flat metal tip and white base with two wires attached to the back.
- Pull out the ignitor: Hold the base and gently unplug it from the wiring harness. Never hold the metal tip as it’s incredibly delicate.
- Inspect it for damage: Take a close look at the base. Can you see any cracks? Also, check for chipping, bends, and broken parts. If you spot any of these, the ignitor might be compromised and thus needs replacement.
- Test it for electrical conductivity: you need a multimeter for this step. Set the meter to resistance (ohms) and place the leads into the plug, one in each hole. Then take the reading. A normally function ignitor will give a reading between 40 ohms and 200 ohms. If it doesn’t register any resistance or has very low resistance, i.e., 0-20 or less, you have a bad ignitor that you must replace. Otherwise, you just need to clean it.
How to Clean a Furnace Ignitor
Still holding the ignitor in your hand and with the power and gas off, find a source of compressed air and blow it gently to remove the dirt and dirt covering the metal surface.
Then put it back in the furnace, turn back power and gas, and switch on the furnace to see if it works. If it doesn’t, replace it.
The good news is that replacing the ignitor is as easy as cleaning it. The most important thing is to find the perfect replacement. Once you have one, just put it in place of the old one and light eh furnace to continue heating your home.
If your furnace ignitor is not glowing, you have low gas pressure, a dirty ignitor, or a defective ignitor that needs replacing. It’s in your best interest to fix the issue fast because the furnace may not start until the ignitor is functional.