Why Lennox Furnace Not Igniting

The furnace is a crucial piece of equipment in your home to help maintain the ideal temperature and provide warmth for you and your family. Even though furnaces are built to last, they can malfunction or break down over time. Lennox furnaces are no exception and can sometimes fail to ignite.

Lennox Furnace not igniting can be due to lack of power, a clogged filter, blocked vent, damaged motor or thermostat, or pilot light being out. Quick fixes to these issues include inspecting and repairing the fuse, cleaning the filter and vent, replacing damaged parts, and igniting the pilot light.

As a rule of thumb, you shouldn’t ignore these problems, as they can lead to further complications when left unfixed. Keep reading for more insights into why your Lennox furnace isn’t igniting and what you can do to fix it.

1. The Furnace Isn’t Getting Power

A Lennox furnace is designed to run on electricity; it won’t ignite without adequate power. This is especially true if you’re using the equipment while the electricity is out (some furnaces require both elements to be on, so they won’t work during a power outage).

How To Fix

You can fix your Lennox furnace by checking its primary power source. First, verify the circuit breakers are working correctly. If so, check for power at the relay or fuse box, located around your home’s breaker panel.

If all of these things check out fine, then there may be an issue with the wiring in your home. It’s best to call an electrician who can inspect further and get everything running again soon.

Caution: Never touch your Lennox furnace’s wiring or internal parts while it’s still connected to the power supply. You risk incurring personal injury and causing further damage to the furnace.

Read: Lennox Furnace Problems

2. The Furnace Filter Is Clogged or Dirty

One major cause of your Lennox furnace not igniting is a clogged or dirty filter. This prevents air from reaching the furnace, which prevents it from firing up.

Also, a dirty filter can lead to dirt and dust accumulation in your home. Over time, it may even damage the furnace by causing overheating.

How To Fix

It’s essential to regularly clean and replace your Lennox furnace filter. Also, ensure the filter is not dusty, thick, or located in a spot with limited airflow.

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If your furnace requires filters, be sure to change them every 2-3 months and keep an extra supply at hand. In this case, I recommend the Amazon Basics Merv 11 Furnace Air Filter from Amazon.com. Thanks to its electrostatically charged filter material, it’s highly effective in capturing dust and lint.

Read: Why Lennox Furnace Is Not Staying ON

3. The Vent Is Blocked

If the airflow is obstructed by insulation or other materials, the Lennox furnace won’t draw in the fresh air it requires to ignite.

Usually, when you turn on your furnace and set the thermostat to a particular temperature, the fan will start up. But over time, dust or other objects may accumulate in the ducts or vents, blocking airflow.

How To Fix

You can fix this problem by removing the obstruction and unclogging the vents. This is crucial to do when the vent is blocked, lest you risk further issues with your Lennox furnace.

This may require taking apart some ductwork parts and cleaning them thoroughly before reassembling everything. If you don’t have experience working on furnaces, consider calling a professional HVAC contractor who can perform this task for you.

Read: Why Lennox Furnace Not Igniting?

4. The Draft Motor Is Damaged

The primary function of a draft motor in a furnace is to pull in air and expel it through your home’s vents. If this part is damaged or broken, air won’t be drawn in properly. This may impede the furnace from igniting when it’s time to heat your home.

How To Fix

If your draft motor is broken, it must be replaced. You can do this on your own or hire a professional HVAC contractor to do the job for you.

If you decide to replace the motor on your own, here are six steps to follow:

  1. Turn off the furnace power.
  2. Using a screwdriver, remove the furnace’s front cover. (This is typically located on top of your home’s vents. Depending on your Lennox furnace model, you may need to access different screw locations to remove it.)
  3. Let out the furnace’s wiring from its clips as needed.
  4. Detach the furnace front cover and set it aside for now.
  5. Unplug the old draft motor from your Lennox furnace.
  6. Put in the new draft motor and secure it with screws before plugging it back into the furnace.

Pro Tip: Keep a check on your draft motor regularly. It shouldn’t be dusty or damaged in any way because it affects your furnace’s performance significantly.

Read: Lennox Furnace Error Codes – Troubleshooting Guide

5. The Thermostat Has Malfunctioned

A faulty thermostat can cause numerous problems with your Lennox furnace, including a failure to ignite. If this has happened, something has likely gone wrong with the thermostat itself.

Here are the common signs of a damaged thermostat:

  • The temperature in your home fluctuates a lot.
  • The furnace turns on, but the house doesn’t get warm–even when set to a high temperature.
  • The thermostat is displaying an unusually high or low temperature.

How To Fix

If the thermostat is broken, it needs to be replaced. You can do this independently or hire a professional HVAC contractor to do the job for you (the service provider will give instructions).

Pro Tip: Check if your thermostat requires calibration. This ensures that it accurately displays temperature changes and facilitates proper furnace ignition.

6. The Pilot Light Is Out

When you turn on your Lennox furnace, the pilot light ignites first; then, the entire heating cycle is initiated. Therefore, if there’s no pilot light or it has gone out, then nothing will happen, even when you turn the system on.

How To Fix

This problem can be frustrating to deal with at times, but it’s not hard to fix. Clearing the pilot light and restarting your furnace should only take a few minutes of your time.

Here are the simple steps you need to take if your pilot light has gone out:

  1. Turn off the furnace.
  2. Locate the pilot light control knob or switch (usually located on the side of your furnace).
  3. Flip the breaker to turn off the gas supply.
  4. Light up a matchstick and use it to ignite the pilot light carefully. It should burn well if sufficient gas pressure resides inside the system. 

Once the pilot light ignites, wait for thirty seconds before flipping on your thermostat to start heating your home again. If it still doesn’t work properly, call an emergency HVAC professional immediately, as there could be severe problems with your furnace.

Here’s an excellent video that demonstrates how to light a furnace pilot light:

7. The Limit Switch Is Damaged

Limit switches are used to limit the temperature of your furnace. For example, if the temperature surpasses a certain point, you can program the system to shut off automatically. If this part is broken or working incorrectly, it may be causing issues with your furnace’s ignition.

How To Fix

You need to replace your unit’s limit switch to fix this problem. You can do this on your own or hire a professional HVAC contractor to do the job for you.

For the best results, consult your furnace’s user manual or call customer support to determine the appropriate switch to use.

Read: Why Is My Furnace Beeping?


Whether you’re troubleshooting ignition problems or simply need to maintain your Lennox furnace, there are a few easy-to-recognize warning signs to tell you when something is wrong. 

Moreover, heating systems should be checked overall at least once every year by a professional HVAC contractor. This ensures everything is working correctly and no safety issues are lurking around, which could affect you or your family members adversely.