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Lennox Furnace Troubleshooting - PartsAPS

lennox furnace troubleshooting

Furnaces are generally reliable, but they are prone to many problems, most of which can be prevented with care and maintenance. If your Lennox furnace won't turn on, doesn't give enough heat, or cycles on and off repeatedly, a little troubleshooting can solve the problem without the need for a repair person. See our Lennox furnace troubleshooting guide and error codes.

Lennox Furnace Troubleshooting Guide

Check the Lennox furnace problems and their troubleshooting tips.

Furnace Not Heating

If your furnace is not heating, a circuit breaker or fuse might be the problem. Most likely, the reason is either the electrical system providing power to your furnace has shorted or the power switch has blown. Replace it if switch has blown. Also, try resetting the Lennox furnace’s circuit breaker and fuse. Reset the breaker if it is tripped.

Also, check the igniter. The igniter may have cracks or it is faulty. So, verify the igniter for cracks. If there are cracks, then you have to replace the igniter. If it isn’t cracked, test for continuity by using a multimeter.

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Lennox Furnace Cycling Irregularly

Verify if the problem is with the thermostat. If the thermostat is set incorrectly, it can cause the furnace to cycle on and off too often. If your furnace's thermostat has an adjustable calibration scale, try adjusting the heat anticipator. If this test does not stabilize the furnace, you may have to replace the thermostat.

Not Blowing Hot Air

Issues with the blower motor caused the furnace not to blow hot air. Your blower motor could burn out completely. Check for the blower motor burned out. If it is not the case, then inspect the connecting belt that it has simply broken. You have to test to see if power is reaching the motor. If the motor receiving power, but is not running, then there may be a failure case with the motor. If the motor runs but air doesn't move, the connecting belt has probably broken. You will need to replace the belt.

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Lennox Furnace Blowing Too Much Air

The problem might be with the control board. The control board regulates the amount of voltage that reaches each functioning part. If the relay in the control board that controls the blower motor has failed, it continuously sends the voltage to the motor. However, you have to check the relay and other components in the control board. Replace if necessary.

Check if the contact that controls the blower motor on your thermostat could be stuck closed. If so, your blower motor will run continuously.

Check the continuity of the thermostat with a multimeter. If there is no continuity, consider the issue with the thermostat and replace it.

Furnace Stops Quickly

It might because of the flame sensor problem. The flame sensor in the furnace monitors the burner that detects whether the flame is present or not. If the flame sensor is either defective or dirty, it won't detect the flame. Using a fine abrasive pad, clean the flame sensor if it is dirty. You will need to replace it if it is faulty.

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Inducer Motor Problem

Once the thermostat calls for heat, the inducer motor comes on to ensure that there is no restriction in the exhaust and intake vent. Inducer motor exhausts the flue gases out of your house when your furnace is running. When the inducer motor is not working, your furnace also stops working. The Inducer motor is placed on the top compartment of the Lennox furnace. Simply touch the inducer motor to test it. If you feel too hot, indicates that it is burnt. Replace it immediately.

Too often, you have to check the air filter. A clogged filter is one of the primary causes of your Lennox furnace problems. A dirty filter tends to abnormal pressure on your unit. Hence, keep the filter clean and dirt-free for running the furnace well and efficiently.

Lennox Furnace Error Codes

Lennox furnaces are designed with two LED lights that will in various patterns to help you diagnose issues. If two LEDs flashing together, it means the unit is running normally. Here is a Lennox error code list you might encounter:

LED 1 - slow flashing and LED 2 - continuous: Indicates that the high limit switch is open.

LED 1 - slow flashing, LED 2 - off: 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 and slow flashing: There is a flame failure.

LED 1 & 2 - alternating and quick flashing: Your furnace not having enough voltage.

LED 1 - slow flashing, LED 2 - fast flashing: There might be a low flame.

LED 1 - fast flashing & LED 2 - slow flashing: The furnace's polarity is reversed.     

Final Thoughts

That's all about our Lennox furnace troubleshooting tips for common problems. If the above guide did not helped to fix your problems, then call a local HVAC technician to get your furnace operating again. Moreover, you can refer to the Lennox troubleshooting manual while fixing your furnace problems. 

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