Lennox Furnace Error Code E180

E180 indicates that the outdoor air temperature sensor has either shorted or is sending a signal outside the expected resistance range. The furnace control board monitors this sensor continuously, and when the reading is implausible or indicates a short circuit, it locks out the sensor input and displays E180. The sensor pack typically needs to be tested with a multimeter and compared against the resistance chart in the installation instructions, and replaced if it is out of spec.

A power cycle may temporarily clear the E180 code, but if the outdoor temperature sensor is genuinely shorted or out of range, the code will return as soon as the control board re-evaluates the sensor circuit. Resetting is useful only to confirm whether the fault is intermittent. A permanent fix requires diagnosing and correcting the underlying sensor or wiring issue.

If only the outdoor temperature sensor pack needs replacement, parts typically range from around $20 to $80 depending on the specific Lennox model, with labor adding $75 to $200 depending on your region and the technician's rates. If the fault turns out to be a damaged wiring harness or a control board issue, costs can increase significantly. Getting a diagnostic call from a licensed HVAC technician first is the best way to get an accurate estimate for your specific situation.

A knowledgeable DIYer can inspect the sensor wiring and connector for obvious damage or corrosion and reseat any loose connections. However, confirming a sensor failure requires a multimeter and access to the resistance-to-temperature chart for the specific unit. If the sensor pack needs replacement, the repair involves working with low-voltage wiring and locating the correct replacement part, which is manageable for someone with basic electrical comfort but may be better left to a technician if there is any uncertainty.

The furnace may continue to operate in a degraded or limited mode while E180 is active, but it will not be able to use outdoor temperature data to optimize heating performance. Running the unit for an extended period without a working outdoor sensor can reduce efficiency and may affect staging or auxiliary heat decisions. It is best to have the sensor repaired promptly rather than ignoring the fault.