Lennox HVAC Error Code E42: How to Fix It

Medium 30-60 minutes (diagnosis), 2-4 hours (if replacement needed) Medium Severity Verified June 2026
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Error Code
E42
Brand
Lennox
Product Type
hvac
Severity
Medium
DIY Difficulty
Medium
Estimated Fix Time
30-60 minutes (diagnosis), 2-4 hours (if replacement needed)
Error code E42 on your Lennox HVAC system indicates a problem with the electronic expansion valve (EXV), which may be stuck or faulty. This can cause improper refrigerant flow, reducing heating or cooling performance. Follow the steps below to diagnose and resolve the issue.
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Tools You'll Need

How to Fix Error Code E42

  1. Power Down the System

    Always shut off power before working on HVAC equipment to prevent electric shock.

  2. Inspect the EXV Wiring and Connections

  3. Check the EXV Coil Resistance

    Use a multimeter with proper safety precautions. Do not touch live circuits.

  4. Verify Control Board Output

    Work carefully around live voltage. If unsure, call a professional.

  5. Inspect the EXV for Mechanical Sticking

    Do not hit the valve too hard as it may damage the refrigerant lines.

  6. Replace the EXV if Necessary

    Refrigerant work requires EPA certification and specialized tools. Do not attempt unless you are trained.

Parts You May Need

Electronic Expansion Valve (EXV) Coil
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Electronic Expansion Valve (EXV) Assembly
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Electronic Expansion Valve (EXV) Coil
Check Price on Amazon
Electronic Expansion Valve (EXV) Assembly
Check Price on Amazon
Electronic Expansion Valve (EXV) Coil
Check Price on Amazon
Electronic Expansion Valve (EXV) Assembly
Check Price on Amazon
Electronic Expansion Valve (EXV) Coil
Check Price on Amazon
Electronic Expansion Valve (EXV) Assembly
Check Price on Amazon
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When to Call a Professional

If you lack HVAC experience, do not have a multimeter, or if the EXV replacement is needed (requires refrigerant handling), call a licensed HVAC technician. This error often requires professional repair.

Frequently Asked Questions

What does Lennox error code E42 mean?
It indicates a fault with the electronic expansion valve (EXV), which is stuck or not functioning correctly, affecting refrigerant flow.
Can I drive my car with error code E42?
Error code E42 is specific to Lennox HVAC systems, not vehicles. For automotive, consult your vehicle's manual.
How much does it cost to fix Lennox error E42?
DIY repair costs are minimal (wiring or coil). Professional replacement of the EXV typically ranges from $400 to $800, including labor and refrigerant.
Is it safe to reset the system to clear the error?
You can try a power reset (turn off breaker for 5 minutes), but if the underlying issue persists, the error will return. Diagnosis is necessary.
Can a dirty air filter cause error code E42?
A dirty filter can cause pressure imbalances, but E42 specifically points to an EXV fault. However, always check and replace dirty filters as part of troubleshooting.

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