Lennox SLP98UHV Error Code E 180: Outdoor Air Sensor Failure
What Does Code E 180 Mean?
Error code E180 on the Lennox SLP98UHV indicates an outdoor air sensor failure. The sensor is either shorted or reading a value outside its expected range. A useful detail: this code only appears for a shorted or out-of-range sensor — if the sensor is simply disconnected, the control generates no error at all.
The outdoor air temperature sensor feeds data the SureLight control uses to fine-tune the furnace's variable-capacity operation. Knowing the outdoor temperature lets the system anticipate heating load and adjust its firing rate proactively. Without valid data, the furnace falls back on indoor temperature feedback, so it may be slightly less responsive to changing outdoor conditions but still heats normally. This makes E180 a low-severity, comfort-optimization sensor fault rather than a safety or no-heat condition — quite different from the control-board hardware codes or the communication-bus faults elsewhere in this series.
Because the furnace keeps running, this is not an urgent repair. A technician should compare the sensor's resistance against the temperature/resistance chart in the installation instructions to confirm it has failed, and replace it to restore full outdoor-temperature optimization.
What You'll Notice
- E 180 shown in the furnace control's error code recall menu
- The furnace continues to heat normally with no lockout or shutdown
- Comfort optimization based on outdoor temperature is reduced
- Modulation or staging may feel slightly less responsive to sudden weather changes
- No other error codes accompany the E180 in a straightforward case
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Outdoor temperature sensor shorted or wiring damaged | Most common | ✗ Call a pro → |
How This Is Diagnosed
A technician confirms E180 by noting that the furnace still runs and by reading the error recall to see the outdoor sensor flagged. Because the code only sets for a shorted or out-of-range reading and not for a disconnected sensor, the technician measures the sensor's resistance and compares it against the temperature/resistance chart in the installation instructions for the current outdoor temperature.
If the resistance is out of range or reads as a short, the sensor or its wiring has failed and the sensor is replaced. If the resistance matches the chart, the technician inspects the sensor wiring and connections for damage. This is a low-priority diagnostic that does not require shutting the furnace down.
When to Call a Professional
This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:
- The outdoor temperature sensor needs to be tested against the resistance chart and replaced
- You want to restore outdoor-temperature-based performance optimization
- The sensor wiring may be damaged and needs inspection
- E180 persists after any recent outdoor-unit or sensor service
Frequently Asked Questions
Is it safe to keep running the furnace with E180?
Yes. E180 is a low-severity sensor fault. The furnace continues to heat safely; it just cannot use outdoor temperature data to optimize its variable-capacity operation until the sensor is repaired.
Why did the code appear if the sensor is just unplugged?
It would not. E180 only sets when the sensor is shorted or reading an impossible value. A simply disconnected sensor produces no error, so the presence of E180 points to a failed sensor or damaged wiring rather than a loose plug.
Will I notice a difference in heating with this code active?
Most homeowners notice little or nothing. The furnace still heats using indoor temperature feedback; it may just be slightly less proactive about adjusting its output when outdoor conditions change quickly.
✓ Verified against manufacturer service manual — March 2026