Lennox Furnace Troubleshooting Guide

Lennox furnace problems may vary from simple DIY fixes every homeowners can do to complicated repairs that require a professional HVAC technician. We will start with the simplest problems and then for more complex issues. This quick Lennox furnace troubleshooting guide will show you what exactly you need to know about Lennox error codes, how to change the furnace filter and more.

The best place to start your Lennox furnace troubleshooting is with the filter, as a clogged filter is one of the primary causes of a furnace problems. It’s also the most common furnace problems.

Dirty furnace filter can lead to abnormal pressure on your furnace, increase the utility bill and reduce the life-span of your system. Keeping your filter clean and dirt free is key to it running well and efficiently.

Lennox furnace troubleshooting guide – Change the air filter

Lennox furnace filter should be changed regularly within the the heating season, and here’s how you do that.

Check your Lennox owner’s manual to recognise the proper filter you need for your particular Lennox furnace model.

To be able to replace the Lennox furnace filter, you’ll need to find the filter cabinet. The filter cabinet is commonly found around the return air duct and furnace.

After getting the filter cabinet, remove the metal door on the face of the cabinet, and set it aside. Remove the old filter and insert the new filter, find the arrows on the new filter and use them as a guideline for placing it, and then slide it into place. Once the air filter is in position, replace the filter cabinet door securely.

How to reset a Lennox furnace

You can reset your Lennox furnace just by shut down the electric power to the system through the circuit breaker. Leave it off around 30 seconds and then turn it back on.

That should clear the board and your furnace will attempt to restart so you can watch to see what’s happening. Be sure to remember the Lennox furnace error code is giving you before you shut-off the power. This code are going to be deleted once the unit is shut down.

Lennox furnace error codes

Here’s a list of Lennox furnace error codes that might come up:

  • LED 1-slow flashing; LED 2-continuous = the high limit switch is open.
  • LED 1-slow flashing; LED 2-off = there was a flame detected with no gas.
  • LED 1-off; LED 2-slow flashing = draft inducer is not operating or the pressure switch circuit has closed.
  • LED 1 & 2-alternating, slow flashing = there’s been a flame failure.
  • LED 1 & 2-alternating, quick flashing = the furnace does not have enough voltage.
  • LED 1-slow flashing; LED 2-fast flashing = the flame is low.
  • LED 1-fast flashing; LED 2-slow flashing = the furnaces polarity is reversed.

If both LEDs are flashing together slowly, it means the furnace is operating normally.

Lennox furnace troubleshooting guide – Check the Thermostat

Here are a few Lennox thermostat checks:

  • If the thermostat needs new batteries, replace them.
  • Make sure the thermostat is set to heat.
  • Make sure the date and time is correct.
  • Check the location of your thermostat and make sure it isn’t getting any fake diagnosis from any heat source. If the thermostat is diagnosing the wrong input, it can provide the wrong output.

Lennox furnace troubleshooting guide – Blower problems

If the Lennox furnace is making an unusual noises it is likely the blower belt or the blower itself. In some cases fixing this blower problem can be just lubricating it. But the best way to fix this Lennox furnace problem is call a qualified HVAC technician to inspect and diagnose the system.

If the above Lennox furnace troubleshooting guide did not stop your issue, then call your local HVAC professional to get your Lennox furnace working again.

About Mas Broto

Have been in the heating and air conditioning (HVAC) industry for over 20 years. He is person that will grow and thrive to learn more about the HVAC industry throughout his career. Mas Broto is also a blogger, who's dedicated to bringing you the best knowledge to get ahead in the game of life.