Lennox E311 Error Code: Restricted airflow, heat rate reduced
Updated October 2026 · Sourced from Lennox documentation
🧭 Check a few things first
The control reports restricted airflow in heating and reduces the firing rate to match the available cfm.
Is it safe to keep running? Check the steps below first. Call a licensed HVAC technician if the code continues after a clean filter and open vents. The ductwork may need work.
E311 at a glance
| Code / how it shows | Meaning | Applies to |
|---|---|---|
| E311 Shown as an E code on the 7-segment display of the integrated control | Restricted airflow, heat rate reduced | Lennox SL280UHVK two-stage variable-speed furnace (integrated control, 7-segment display) |
Check this first
Only steps a homeowner can do safely. Do not open electrical panels or the burner area.
- Replace a dirty air filter, then restore power and see if the code returns.
- Make sure supply and return vents are open and not blocked by furniture or rugs.
🛑 Stop and call a licensed pro if
- Call a licensed HVAC technician if the code continues after a clean filter and open vents. The ductwork may need work.
- You smell gas. Leave the house, do not touch switches, and call your gas utility from outside.
- Flame rollout, limit or pressure switch codes that come back after one reset.
- Anything involving the control board, gas valve, flame sensor, igniter or venting.
- A carbon monoxide alarm sounds. Get everyone outside and call 911 or the fire department.
Safe first steps for any Lennox code
- Count the LED flashes through the blower door window before you switch anything off. Cutting power can clear the code.
- Replace or clean the furnace air filter.
- Check the thermostat: correct mode, set above room temperature, and fresh batteries.
- Make sure the furnace power switch and breaker are on. If the furnace has locked out, turning the power off and back on once restarts it.
- Make sure the gas valve is in the ON position, following the lighting instructions on the furnace label only.
- On high-efficiency furnaces, look at the outside vent and intake pipes for snow, ice, leaves or nests (look only, do not take pipes apart).
Source: Lennox SL280UHVK Installation Instructions 508553-01 (01/2025), Ignition Control Diagnostic Codes (continued), p.37. Codes are series-specific, so your unit's own manual is the final word. Reviewed October 2026.
Shaun Cain · Certified HVAC & Refrigeration Technician · Ask an HVAC technician
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