Lennox Furnace Error Code E276

E276 indicates that airflow through the system during cooling or continuous fan mode is falling below the configured CFM target. The furnace control board detects this shortfall and places the indoor blower into cutback mode, where it continues running at reduced capacity. The fault points to a restriction somewhere in the air distribution system, most commonly a dirty filter or blocked ductwork.

Resetting the furnace may temporarily clear the fault code, but E276 will return if the underlying airflow restriction is not corrected. The control board will continue to detect the CFM shortfall each time the blower runs in cooling or continuous fan mode. Address the physical cause of the restriction first, then reset the system.

The cost depends on the cause. A replacement air filter typically runs between $10 and $40 depending on type and rating, making it a low-cost first step. If ductwork repairs or modifications are needed, costs can range from $150 to $1,000 or more depending on the extent of the work and local labor rates. A technician diagnostic visit to identify and confirm the restriction source generally runs between $75 and $150.

Start by replacing the air filter, since a clogged filter is the most common cause. After replacing the filter, check that all supply and return registers throughout the home are fully open and unobstructed. If the fault persists, inspect accessible ductwork for collapsed sections, kinks, or undersized runs that could be restricting airflow below the blower's target CFM.

E276 is a protective fault rather than an immediate safety emergency. Cutback mode keeps the blower running at reduced speed, which prevents complete air stagnation and helps protect the heat exchanger from overheating. However, running in cutback mode for extended periods reduces system efficiency and can increase wear on components, so the restriction should be corrected promptly.