Lennox Furnace Error Code E310

E310 on a Lennox furnace indicates a discharge air temperature sensor failure. The sensor, a thermistor that monitors the temperature of heated air leaving the heat exchanger, is sending a signal that is either shorted or outside the valid resistance range. The furnace control board cannot use an invalid reading to safely manage operation, so it flags this error code. The sensor, its wiring, or the connector terminals are the most likely sources of the problem.

Running the furnace while E310 is active is not recommended. The discharge air temperature sensor helps the control board verify that supply air temperatures remain within safe limits. Without a valid sensor reading, the board cannot detect overheating conditions, which could allow the heat exchanger to overheat and potentially cause damage or a safety shutdown. It is best to resolve the error before resuming normal furnace operation.

Resetting the furnace by cycling the power may temporarily clear the E310 code, but the error will return if the underlying sensor fault is still present. A reset does not repair a shorted or out-of-range thermistor, damaged wiring, or corroded connector pins. Persistent reappearance of E310 after a reset confirms that a physical component issue needs to be diagnosed and corrected before the furnace will operate reliably.

A knowledgeable DIYer can perform basic diagnostics, such as inspecting wiring and measuring sensor resistance with a multimeter and comparing it to the temperature-resistance chart in the furnace installation instructions. If the sensor is confirmed faulty, replacing it is a straightforward task if you are comfortable working with HVAC components and low-voltage wiring. However, if the control board or refrigerant system is involved, a licensed HVAC technician should handle the repair.

Repair costs depend on the cause. If only the discharge air temperature sensor needs replacement, parts typically range from $15 to $60, and a technician visit to diagnose and replace the sensor generally adds $75 to $200 in labor. If the control board is at fault, board replacement costs can range from $200 to $600 or more depending on the model. Getting a diagnostic visit from a certified HVAC technician will give you an accurate estimate for your specific unit.