Lennox HVAC Error Code E24: How to Fix It

Medium 30-60 minutes Medium Severity Verified June 2026
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Error Code
E24
Brand
Lennox
Product Type
hvac
Severity
Medium
DIY Difficulty
Medium
Estimated Fix Time
30-60 minutes
Error code E24 on your Lennox HVAC system indicates a fault with the return air temperature sensor. This sensor monitors the temperature of air returning to the unit, and a failure can cause improper system operation. Follow these steps to diagnose and resolve the issue.
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Tools You'll Need

How to Fix Error Code E24

  1. Turn Off Power to the System

    Always shut off power before working on HVAC components to avoid electrical shock.

  2. Locate the Return Air Temperature Sensor

  3. Inspect the Sensor and Wiring

  4. Test the Sensor Resistance

    Handle the sensor carefully; it is sensitive to static electricity.

  5. Replace the Sensor if Faulty

    Ensure the replacement sensor matches the original specifications.

  6. Restore Power and Test the System

Parts You May Need

Return air temperature sensor
Check Price on Amazon
Return air temperature sensor
Check Price on Amazon
Return air temperature sensor
Check Price on Amazon
Return air temperature sensor
Check Price on Amazon
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When to Call a Professional

If the sensor tests good and connections are secure but the error persists, the control board or wiring harness may be faulty. Call a professional HVAC technician for advanced diagnostics and repair.

Frequently Asked Questions

What does Lennox error code E24 mean?
Error code E24 indicates a fault with the return air temperature sensor. The sensor is either faulty, disconnected, or has a wiring issue.
Can I still use my HVAC system with error E24?
It's not recommended. The system may operate inefficiently or could shut down to prevent damage. Fix the sensor issue before regular use.
How do I test the return air temperature sensor?
Use a multimeter to measure resistance across the sensor terminals. At room temperature (77°F), it should read around 10k ohms. Refer to your model's specifications.
Where is the return air temperature sensor located?
It is usually mounted in the return air duct near the air handler or furnace. Look for a small sensor with two wires attached to the duct.
How much does it cost to replace the return air temperature sensor?
The sensor part typically costs $20-$50. If you hire a technician, labor may add $100-$200.

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