Lennox Furnace Error Code E215

E215 indicates an outdoor air sensor failure caused by a shorted or out-of-range signal from the sensor. The furnace control board reads the sensor's resistance to determine outdoor temperature, and when that resistance falls outside the expected range, the board flags E215. Notably, the error only appears when the sensor is connected but reading incorrectly. A disconnected sensor does not trigger this code.

E215 relates to the outdoor air sensor and does not directly affect combustion safety or heat exchanger operation. In most cases the furnace will continue to heat your home, though features that depend on outdoor temperature data may not function correctly. It is still advisable to diagnose and correct the fault in a timely manner to ensure the system operates as designed and to prevent any related control issues from developing.

If only the outdoor air sensor needs to be replaced, the repair is generally straightforward and parts costs are typically in the range of $15 to $60 depending on the specific sensor model. If a service technician is needed, labor charges will add to this cost, typically bringing the total into the $100 to $250 range depending on local rates and diagnostic time. Wiring repairs are usually on the lower end of that range, while a control board replacement, if ever required, would cost significantly more.

Start by measuring the outdoor sensor's resistance with a multimeter and comparing the value to the temperature-resistance chart in the installation instructions. If the resistance does not match the expected value for the current outdoor temperature, replace the sensor. Also inspect the wiring between the sensor and the control board for shorts, corrosion, or loose connections, as faulty wiring can cause the same fault without the sensor itself being defective.

A reset may temporarily clear the displayed code, but if the underlying sensor or wiring fault is still present, E215 will return once the control board re-evaluates the sensor input. A lasting fix requires correcting the root cause, whether that is replacing a failed thermistor, repairing damaged wiring, or cleaning corroded connections.