Lennox Furnace Error Code E275

E275 indicates that the furnace has detected restricted airflow and has entered blower cutback mode. The control board reduces the heat output rate to match the lower airflow capacity, protecting the heat exchanger from overheating. The furnace continues to operate but at reduced heating performance until the airflow restriction is identified and corrected.

E275 is a protective response rather than an immediate safety hazard. The furnace automatically reduces its heat output to prevent the heat exchanger from overheating due to restricted airflow. However, running continuously in cutback mode puts additional stress on system components over time, so the underlying airflow restriction should be addressed promptly rather than left unresolved.

Repair costs vary depending on the cause. Replacing an air filter is typically inexpensive, ranging from a few dollars to around $30 depending on the filter type. If ductwork repairs or modifications are needed, costs can range from $150 to $600 or more depending on the scope of work. A service call to diagnose and repair the issue professionally generally falls in the $80 to $200 range before parts.

Start by replacing the air filter, which is the most common cause of this error. After replacing the filter, check that all supply and return registers throughout the home are fully open and not blocked by furniture or rugs. If those steps do not resolve the issue, inspect accessible ductwork for collapsed flex ducts or other obstructions, and contact a technician if the ductwork appears undersized or damaged.

Resetting the furnace may temporarily clear the E275 alert, but the code will return if the airflow restriction is not corrected first. The control board continuously monitors airflow conditions and will re-enter cutback mode as soon as it detects insufficient air movement again. A permanent resolution requires finding and fixing the source of the restriction, such as a clogged filter or blocked ductwork.