Lennox E291: heating airflow restricted below the minimum

Furnace control display or LED

E291

“Heat air flow restricted below the minimum.”

SL280*V, SL280*NV, SL297*NV, EL296*V, EL297*V · 1116-L4 p. 26; 508150-02 p. 48; 1802-L1 p. 19; 1126-L5 p. 18; 100088 p. 41
Technician

What it means

E291 means the control found the airflow during heating below the minimum. In the tables for the SL280, SL297, EL296V and EL297V the action is: check for a dirty filter and air flow restriction, and check blower performance. The furnace goes into a 1-hour soft lockout, and the code clears when a heat call finishes successfully 1126-L5, p. 18; 1116-L4, p. 26. The SLP98, SLP99 and G71MPP tables describe the code as restricted air flow, with cubic feet per minute lower than what the minimum firing rate needs, and give “Check for dirty filter, unit air flow restriction, blower performance.” as the action 508589-02, p. 47.

Not every edition lists E291. The 07/2026 SL297UHNVK instructions and the 06/2026 EL297DFVK instructions have no E291 in their code tables 508585-02, pp. 47–52; 508583-01, pp. 50–55. Restricted airflow appears there as E311, “Heat rate reduced to match indoor blower air flow.”, a warning: the blower is in cutback mode due to restricted airflow and the furnace reduces its firing rate to match the available airflow 508585-02, p. 51.

Lennox’s thermostat alert 291 is “GF Heat Airflow Below Min”, priority Service Urgent: the heating airflow is below the minimum required level and the system goes into Watchguard mode. Its checks are dirty air filters and other air flow restrictions, and blower performance; it clears automatically when a heat call ends successfully 100017, p. 24. Lennox’s documents do not say that alert 291 and display code E291 report the same event.

Check these first

Lennox’s owner’s manuals have no code table and give no steps for E291. What they give is a general list for a unit that will not operate, to work through before calling a Lennox service technician. In the SLP99DFVK manual the order is:

Check that the electrical disconnect switches are ON 508590-01, p. 5.
Check the room thermostat for proper setting 508590-01, p. 5.
Replace any blown fuses or reset circuit breakers 508590-01, p. 5.
Check that the gas valve is ON 508590-01, p. 5. Its switch is behind the outer access panel; the manual’s gas valve steps set the thermostat to the lowest setting and turn off all electrical power to the unit before that panel comes off, and the switch is moved by hand only, never with tools 508590-01, p. 4.
Check that the air filter is not plugged, which would limit air flow 508590-01, p. 5. The SLP99DFVK manual says its filters are installed external to the unit, should be inspected monthly, and that a filter must be in place when the unit is operating 508590-01, p. 4. Before any service or maintenance, it says to turn the electrical power to the unit OFF at the disconnect switch 508590-01, p. 2.
Check that gas is turned on at the meter 508590-01, p. 5.
Check that the manual main shut-off valve is open 508590-01, p. 5.

Then record the model and serial number from the nameplate and call 508590-01, p. 5. The list is not tied to any code. More on it, and on how other Lennox manuals word it: owner checks before a service call.

The manual’s Maintenance section says the maintenance procedures should only be conducted by a licensed professional service technician, and not to attempt to service the unit in any way 508590-01, p. 5.

When to call a licensed technician

The checks in the E291 row: a dirty filter, air flow restriction in the unit, and blower performance 1126-L5, p. 18; 508589-02, p. 47.
The alert guide’s checks for alert 291: dirty air filters and other air flow restrictions, and blower performance 100017, p. 24.
The furnace goes into the 1-hour soft lockout 1126-L5, p. 18.
Any work inside the furnace 508590-01, p. 5.
The furnace still will not run after the checklist 508590-01, p. 5.
E291 keeps coming back after it clears. The owner’s manuals give no step for that; these pages send it to the technician.

Notes for different models

Series or document	Code	Wording	Source
SL280V, SL280NV, SL297NV, EL296V, EL297*V (editions that list it)	E291	“Heat air flow restricted below the minimum.” Action ends “1-hour soft lockout. Cleared when heat call finishes successfully.”	1116-L4, p. 26; 508150-02, p. 48; 1802-L1, p. 19; 1126-L5, p. 18; 100088, p. 41
SLP98V, SLP99V, G71MPP	E291	“Restricted air flow - Cubic feet per minute is lower than what is needed for minimum firing rate.” No lockout in the action.	508589-02, p. 47; 506610-01, p. 63; 506509-01, p. 66
SL297UHNVK (07/2026), EL297DFVK (06/2026)	no E291	Restricted airflow appears as E311, “Heat rate reduced to match indoor blower air flow.”	508585-02, p. 51; 508583-01, pp. 50–55
Lennox thermostat alert table	291	“GF Heat Airflow Below Min”, Service Urgent	100017, p. 24

E312, in the same tables, covers airflow in cooling or continuous fan mode: “Restricted air flow in cooling or continuous fan mode is lower than cfm setting.”, a warning only 508585-02, p. 52.