Lennox Furnace Code E291
Warning
Restricted air flow. The blower is moving fewer cubic feet per minute than the furnace needs even at its minimum firing rate.
Manual wording: “Restricted air flow - Cubic feet per minute is lower than what is needed for minimum firing rate. Check for dirty filter, unit air flow restriction, blower performance.”
Documented for: SLP98UHV series
Likely causes, most common first
- Dirty air filter
- Restricted, undersized or partially collapsed ductwork
- Blower wheel dirty or blower performance degraded
- Closed or blocked registers
What you can safely check yourself
- Check the air filter and replace it if it is dirty
- Make sure supply and return registers throughout the house are open and unblocked
- Check that the return grille is not covered
When to call a technician
If a clean filter and open registers do not clear it, the duct system or blower needs to be evaluated by a technician.
A Lennox furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Source
- SLP98UHV Service Literature (Corp. 1029-L7), Table 14 - LED 7 Segment Status / Error Code and Integrated Control Diagnostic Codes (Lennox Industries Inc., SLP98UHV series variable-capacity communicating gas furnace (66,000-132,000 Btuh)) · checked 2026-08-25