How to Read Lennox Furnace Codes: The Easiest Way To Find Out What’s Wrong

You’re in the middle of a hot summer day, and you start thinking about getting home from work as soon as possible. You know it’s still early, but your thermostat is telling you that the house isn’t going to get much cooler any time soon. You glance at the furnace panel and see a few blinking lights that look like numbers and maybe a few symbols–but what do those mean? You check your user manual, but the troubleshooting section doesn’t seem to have anything about those codes. You try googling some keywords about them, but nothing useful comes up. How to read Lennox furnace Codes? Well, luckily for you, we have some answers you’ll find useful! Keep reading to learn more.

What Do Lennox Furnace Codes Mean?

Furnace codes can vary between manufacturers, but generally, a flashing furnace code indicates that there is some kind of problem. The specific code will tell you a little more about what that problem is and what you’ll need to do to fix it. Furnace codes may be represented as a combination of numbers and/or letters. For example, E3, CO, or C3. Lennox furnace codes that flash and have a letter, like “E”, generally relate to a problem with the furnace’s energy source, and a number, like “3”, relates to a problem with something in the furnace’s control system. The furnace will display a code when something goes wrong, like a clogged filter, a broken wire, or a blocked air vent. Codes can be either a continuous problem or a one-time error.

So, How Do You Read Lennox Furnace Codes?

This might vary depending on your furnace type, but for Lennox, the first step is to make sure that the furnace is on. For example, some models have a start/stop button and others have an on/off switch. Next, locate the display panel and look for the error code. Some models have a light that flashes when there is a problem, while others have a digital panel with a code. An audible alarm might sound when the code is displayed. If you have a model that doesn’t have an error code, you can look inside the furnace’s control box to find the circuit breaker that is responsible for the furnace. That should tell you what the problem is.

When Should You Read the Code?

You should always read the code when the furnace is on and having some kind of problem. If the furnace is working normally, there will be no code to read. Always be safe when working with your furnace. Don’t touch anything that might be live, like wires, breakers, or the furnace blower motor. If you aren’t sure what the code means, write it down and look it up online. There are a couple of good websites where you can enter the code and find out what it is. If there’s a problem with the furnace’s control system, check the wiring diagram. You might be able to fix it yourself by simply re-connecting one of the wires. If the problem is with the furnace’s energy source, like the circuit breaker, you’ll have to call a professional.

Common Codes and Their Meanings

There are a few different ways to tell what the code is. Some will have letters and numbers, like “E3”, while others will have a one-word description like “C33”. However, regardless of the code, the method of reading it is the same. It’s best to write it down so you don’t forget it. Stored Energy: This is the most common problem. Your furnace has too much energy in it, like a capacitor. You need to reset the furnace so that it resets itself. Overload: This is caused by too much heat. The furnace’s blower fan, igniter, or main circuit breaker may be broken. Overcurrent: Something is wrong with the control board. Overheat: The furnace is too hot. There might be a problem with the igniter or the circuit board.

Error Code 15: Blower Problem

The blower fan, which is located inside the furnace, is very important because it circulates the air through your home. If the blower is having problems, you’ll see this code. There are a few different things that could be causing this, like a broken fan belt, clogged air filter, or a broken blower motor. To fix this, you’ll need to remove the furnace and take a look at the blower fan. Sometimes, cleaning the fan or replacing the belt will do the trick. If not, you may need to replace the blower motor.

Error Code 17: Damper Problem

The damper is a flap inside the furnace that controls the flow of hot air. If there’s a problem with the damper, the furnace overheats and burns out. To find out if this is the problem, remove the furnace, and look at the air vent. If it’s blocked, you can clear it out. If it’s not blocked, you’ll need a furnace repairman.

Error Code 19: Combustion Problem

If something is wrong with the furnace’s burners, this is what you’ll see on the display panel. If the burners are broken, you can replace them, but if there’s something wrong with their controls, you need a furnace repairman.


Lennox furnaces are reliable and efficient, but they can break down from time to time. If you’re having issues with your furnace, it’s important to know how to read the codes on your furnace panel, as this can help you identify the issue and take the appropriate action to get it repaired. At the same time, all Lennox furnaces come with a warranty that covers all parts and labor for a year from the date of purchase, so don’t hesitate to call for Lennox furnace repair.