How To Troubleshoot My Lennox Gas Furnace

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You can troubleshot your gas furnace.
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Is your Lennox gas furnace not heating like you expect? Lennox is a well-known name in HVAC systems and has been around since 1895, but that doesn't stop a Lennox furnace from having occasional issues. A little troubleshooting can help you decide if the issue is minor enough to fix yourself or if you need to call in an HVAC professional.

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Check the Thermostat

The home thermostat might not seem like the most important part of your furnace, but issues with the thermostat can keep your heat from running correctly. Verify that the thermostat is set to the "heat" setting just in case it got bumped or turned off. Once you switch it to the "heat" position, give the unit a few minutes to start working, as some are delayed.

If the thermostat doesn't appear to have power, it could need new batteries. Many thermostats use AA batteries or AAA batteries but take a quick look inside yours to determine what type you need. If the batteries are low, the thermostat might be getting some power, but it might not work correctly, so fresh batteries can help.

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Once you're sure the thermostat is turned on and has adequate power, turn the heat setting up to at least 10 degrees higher than the room temperature. Your furnace will only turn on if it's set to a higher temperature than the room. Wait a few minutes to see if the furnace turns on.

Verify It's Getting Power

Even though your Lennox furnace is gas-powered, it still requires electricity for some of its components. Check power sources to make sure your furnace is getting what it needs. Look at the circuit breaker that powers the furnace to see if it flipped. Reset the breaker if needed.

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Furnaces also typically have a power switch on or near the unit. It looks just like a light switch, so someone could accidentally flip it off if he doesn't realize it controls the furnace. Like your light switches, the up position should be "on" for the furnace switch if it was installed correctly. Flip the switch and give your furnace a few minutes to turn on.

Change the Filter

Keeping up with routine maintenance, like changing furnace filters, helps your Lennox gas furnace run smoothly. If you forget to change your furnace filter, it can become clogged with dirt and debris, which restricts airflow. Dirty filters can cause additional damage, especially in newer, energy-efficient furnaces. Some models even shut down if your filter is clogged. Others keep running, but the restricted airflow can decrease output and make it more difficult for the furnace to heat your home.

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If you haven't changed your filter lately, put in a fresh one to see if it helps. Even if you change the filter regularly, take out the current filter to see if it has lots of debris in it.

Look for Error Codes

Many modern furnaces, including Lennox gas furnaces, feature LED lights or other forms of error codes that can indicate a problem. If your unit has lights, they might blink or flicker at different rates to give various error codes. Refer to your owner's manual for specific help in deciphering the error codes to figure out the problem. If it's a problem with an internal part, such as your blower or ignitor, you'll likely need help from an HVAC professional to fix the problem. The error codes can help you anticipate the problem and explain what might be wrong to the HVAC company.

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Shelley Frost combines her love of DIY and writing in her freelance career. She has first-hand experience with tiling, painting, refinishing hardwood floors, installing lighting, roofing and many other home improvement projects. She keeps her DIY skills fresh with regular projects around the house and extensive writing work on the topic.