How To Reset A Lennox Furnace 

If you're experiencing issues with your Lennox furnace, one of the first things recommended by HVAC professionals is to perform a quick reset. Resetting a malfunctioning furnace can often help clear any current settings and get the unit back up and running again.

But how do you reset a Lennox furnace? We have researched this furnace brand, and in this post, we will answer this question for you.

Here are the steps to reset a Lennox furnace:

  1. Turn off the power to the furnace
  2. Remove the front panel of the furnace
  3. Find the reset button
  4. Turn the power back on

Various issues may cause a Lennox furnace to stop working. And sometimes, it can be challenging to find the exact cause, so we will cover them here. Continue reading to learn how to troubleshoot your Lennox furnace.

A home high energy efficient furnace in a basement, How To Reset A Lennox Furnace 

Steps to Reset a Lennox Furnace

1. Turn off the power switch to the furnace

Turn off the power switch on the furnace, which will be located on the side of the control panel--it will look very similar to a wall light switch. Next, go to your circuit breaker, find the switch corresponding to the furnace, and turn it to the "Off" position.

2. Remove the front panel of the furnace

Next, use a flathead screwdriver to unscrew the top and side areas of the furnace. Then lift the front panel off and set it to the side. The panel's location will vary by furnace model, so you may find that the panel is on the side or bottom area of the furnace.

A home high energy efficient furnace in a basement

3. Find the reset button

When removing the front panel of the furnace, look for a raised switch or a button on the side of the control panel area. The limit switch will house the reset button in the middle in many Lennox furnace models. If you aren't sure how to recognize the switch, refer to your user's guide. Press and release the reset button to reset the furnace.

4. Turn the power back on

After pressing the reset button, go to the circuit breaker and turn the switch back to the "On" position. Next, flip the switch on the furnace to power it up again.

You may need to raise the temperature on the thermostat to turn the furnace on. If the reset button solves the problem, you're good to go. If it doesn't, you may need to continue troubleshooting the furnace in accordance with the user's guide.

Want to see how to troubleshoot a Lennox furnace? Check out this video:

Why is my Lennox furnace not working?

Various reasons can play a part in why your Lennox furnace isn't working. The most common reasons include malfunctioning parts, airflow restrictions, and pilot light issues. Let's discuss them in more detail.

Issues with the thermostat

A home Goodman high efficiency furnace with Bradford White Residential gas water heater & an Generalaire humidifier.

The thermostat is responsible for controlling the temperature of the furnace, so when it malfunctions, the furnace may not kick on, or it may cycle on and off. In some cases, the thermostat may need a battery replacement. And in other cases, it may be faulty and in need of replacement itself.

If you notice the furnace cycling on and off or not being able to hold a steady temperature, testing the thermostat may be a good idea. It's also recommended to clean the thermostat sensors using a dusting cloth or soft brush. Sometimes dust can accumulate on the sensors, which can cause issues with the thermostat.

Blown fuses or wires

If your furnace is over 10 to 12 years old, the furnace may have blown an electrical component. For example, if you set the thermostat to the "On" position and the furnace does not come on at all, it usually means that there is an issue with the power supply. Try resetting the furnace, and if this doesn't work, it may be best to reach out to an HVAC technician.

Pilot light issues

Pilot light issues are some of the most common issues that gas and oil-based furnaces face. These flames can go out due to issues with the gas supply, dirty sensors, or drafts. And in most modern furnaces, you can reset the pilot light by turning the switch to the "On" position and pressing the pilot button.

In older furnaces, you may be able to light the pilot manually if it goes out. If it has trouble remaining lit, it could be that the flame sensor is dirty or faulty.

The air filter is dirty

Senior caucasian man changing a folded dirty air filter in the HVAC furnace system in basement of home

A clogged air filter may cause your furnace to shut off due to overheating. When the air filter is clogged, the blower motor goes into overdrive to push air through the filter, meaning that it will work longer than it usually would.

As a result, the limit switch will shut off the furnace to prevent overheating. At some point, this can lead to burnout If the furnace is on the older side.

Gas valve issues

Pipes and valves of a heating system

If you recently had your furnace cleaned or inspected, the issue could be with the gas valve. Sometimes contractors may turn off the gas valve as a safety precaution, especially during the spring and summer seasons. And if the pilot light will not come on, be sure that the gas valve is turned to the "On" position.

The limit switch is burned out

A faulty limit switch can also cause the blower motor to run continuously. As a result, the motor may eventually burn out, causing the furnace to become inoperable.

If you turn on the furnace and there is no sound coming from the motor, the chances are that either the motor or the limit switch has become faulty. And if the limit switch has blown out, an experienced technician can test and replace it if necessary.

The flame sensor is dirty

If the furnace keeps shutting down during operation, the issue could also be with the flame sensor. Over time, the flame sensor can become dirty from soot and debris emitted from the furnace. You can clean this part yourself using a thin piece of sandpaper or a hardwired brush.

Also, if you have your furnace on a maintenance plan, the HVAC technician will typically clean this component for you.

Does a Lennox furnace have a pilot light?

older home has furnace system repaired for the winter

Yes. The current Lennox furnace models operate using oil or gas, which means that they require a pilot light to ignite the darkness inside of the combustion chamber.

How do you reset the pilot light on a Lennox furnace?

Here are the steps to reset the pilot light on a Lennox furnace.

  1. Remove the front panel from the furnace.
  2. Turn the pilot light switch from the "On" position to the "Off" position. Give the furnace about 3 to 5 minutes so that any lingering gas can dissipate.
  3. Next, turn the pilot knob to the "Pilot" position and then simultaneously press down and hold the "Reset" button located on the side of it. You may need to press the button a few times while holding down the pilot knob. Once the flame ignites, release the button. Watch the flame for a couple of minutes to ensure it doesn't go out. Next, place the panel back on the furnace.

What does a blinking red light mean on a Lennox furnace?

A blinking red light on a Lennox furnace can mean a few things. Here are the most common issues that it may indicate:

Issues with the blower motor

Heater exhaust fan inside of furnace

If the red light flashes multiple times within minutes, the chances are that it's an issue with the blower motor. The most common reason is that the motor has either become faulty or is experiencing an electrical failure. It's best to have an HVAC technician look at the motor to replace any bad wires or the motor itself.

Single light blinks three times

If a single light blinks slowly, it often indicates that the Lennox furnace is experiencing a short circuit or has insufficient voltage. Resetting the furnace at the circuit breaker may help with this issue, but it may not solve your problem. Ultimately you'll need to have a technician or electrician inspect the unit and the switch at the circuit breaker for continuity.

Two or more blinking red lights

Multiple blinking red lights often indicate an issue with the gas valve, supply, or igniter control. Sometimes the gas valve may be turned to the "Off" position, and it may be faulty in other cases. It's best to have a licensed technician troubleshoot these types of issues to prevent hazardous conditions in your home.

What does a green flashing light mean on a Lennox furnace?

A blinking green light usually means that the circuit board needs to be replaced or that it is not communicating well with the blower motor (due to blown fuses or wires). In either situation, you'll need to contact an HVAC technician to troubleshoot the electrical issue and replace the board, if necessary.

Wrapping Things Up

Closeup Shot Of Home Furnace Burner Ignited With Crimson Blue Flame

We hope this post has helped explain how to reset and troubleshoot common Lennox furnace issues. Remember, when facing a serious problem, the first thing to do is refer to your user's guide. If you cannot mitigate the issue yourself, then it's best to reach out to the pros for assistance.

Before you go, be sure to check out our other posts:

Does A Furnace Fan Reduce Humidity?

How To Cover Furnace Exhaust Pipe

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One comment

  1. Thermostat downstairs has nothing on it. But the thermostat upstairs is working normally what is the problem, is there a battery in the thermostat downstairs

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