Error Code E 311
Low Lennox EL296UHV Error Code E 311: Heat Rate Reduced to Match Airflow
TL;DR
Your furnace has automatically reduced its heating output because airflow is restricted. This is a warning, not a shutdown. The most common cause is a dirty air filter. Replace your filter and check that all vents are open. If the ductwork is undersized, an HVAC professional may need to modify it. Most likely cause: dirty air filter restricting airflow. Disclaimer
This article is for informational purposes only and does not guarantee the accuracy or completeness of the information provided. Always turn off power and gas supply before attempting any repairs. If you smell gas, leave immediately and call your gas company. Consult a licensed HVAC technician for diagnosis and repair. Any actions taken based on this information are at your own risk. What Does Code E 311 Mean?
Your furnace has automatically reduced its heating output because airflow is restricted. This is a warning, not a shutdown. The most common cause is a dirty air filter. Replace your filter and check that all vents are open. If the ductwork is undersized, an HVAC professional may need to modify it.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Dirty air filter restricting airflow | Most common | ✓ DIY fix → |
| Undersized or restricted ductwork | Common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- Basic troubleshooting did not resolve the error
- You smell gas at any point during the process
- You are not comfortable working around gas lines or electrical components
- The unit needs a gas valve, control board, or motor replacement
✓ Verified against manufacturer service manual — March 2026