Lennox Furnace Error Code E291

E291 indicates that the furnace has detected heat airflow restricted below the minimum required level during a heating cycle. The control board monitors airflow to protect the heat exchanger from overheating and triggers this code when conditions fall short of the threshold. The furnace may shut down the heating sequence until the restriction is resolved. Checking the air filter and blower performance are the recommended first diagnostic steps.

A manual reset may temporarily clear the E291 code and allow the furnace to attempt another heating cycle, but the code will return if the underlying airflow restriction has not been corrected. Resetting without addressing the root cause can lead to repeated shutdowns and potential heat exchanger stress over time. Always resolve the restriction before relying on a reset.

If the fix is simply replacing a clogged air filter, the cost is minimal, typically in the range of a few dollars to around thirty dollars depending on filter type. If the blower motor capacitor needs replacement, repair costs generally fall in the range of eighty to two hundred dollars including labor. A failed blower motor replacement can range from three hundred to six hundred dollars or more depending on the motor and local labor rates. Ductwork repairs vary widely based on the extent and location of the damage.

Start by replacing the air filter if it is dirty or overdue for replacement. Then check that all supply and return registers in the home are fully open and unobstructed. If airflow is still restricted after those steps, the blower motor, capacitor, or blower wheel may need inspection by a technician. Collapsed or disconnected ductwork is another possible cause that requires physical inspection of accessible duct runs.

The furnace shuts down the heating cycle specifically to prevent the heat exchanger from overheating when airflow is insufficient, so continued operation with the restriction in place can damage the heat exchanger. A cracked heat exchanger is a serious and costly failure. It is best to resolve the E291 condition before resuming normal furnace operation.