Lennox Furnace Error Code E252

E252 indicates that the discharge air temperature in gas heating mode has exceeded the safe upper limit. The furnace control board monitors the temperature of air leaving the heat exchanger, and when it gets too high, the system shuts down and displays E252. The most common causes are restricted airflow, an elevated gas input rate, or a blower problem. The issue must be diagnosed and corrected before the furnace will operate safely.

Yes, E252 should be treated as a safety-related fault. Excessive discharge air temperatures can stress and eventually crack the heat exchanger, which can allow combustion gases including carbon monoxide to enter the living space. The furnace's automatic shutdown is a protective response, and running the unit repeatedly while the fault is unresolved increases the risk of permanent heat exchanger damage.

Repair costs depend entirely on the root cause. If a dirty filter or blocked register is the problem, there is little to no cost beyond a replacement filter, which typically runs a few dollars to around twenty dollars. A blower motor capacitor replacement may cost in the range of fifty to one hundred fifty dollars in parts and labor. Blower motor replacement or heat exchanger repair can range from several hundred to over one thousand dollars depending on the component and local labor rates.

Start by checking and replacing the air filter, then confirm that all supply and return registers throughout the home are open and unobstructed. If the filter is clean and airflow appears normal, a technician will need to measure temperature rise, verify manifold gas pressure, and test blower motor performance. Do not continue operating the furnace repeatedly until the root cause is identified, as sustained high discharge temperatures can damage the heat exchanger.

Resetting the furnace may temporarily clear the E252 code and allow the unit to start again, but the error will return if the underlying cause has not been corrected. Simply resetting without addressing airflow, gas input, or blower issues does not resolve the problem. Repeated resets while the fault condition persists can accelerate wear on the heat exchanger and other components.