On the covered Lennox gas furnace, E180 means outdoor air temperature sensor failure. It is shown only if the sensor is shorted or out of range. It clears 30 seconds after the fault recovers. First, look for a damaged or disconnected outdoor sensor wire.
Differential
Likely causes of “Lennox gas furnace code E180”, and how to tell them apart
- 1
A shorted or open outdoor sensor wire
What separates it E180 shows only when the sensor is shorted or out of range
How to confirm Look for a pinched or cut wire along the run to the outdoor unit
- 2
A failed sensor pack
What separates it The wire is intact and the reading is far off
How to confirm Compare the measured resistance with the temperature-resistance chart
- 3
A sensor removed on purpose
What separates it The outdoor sensor was taken away and the setting was not updated
How to confirm Check the About screen for the sensor status
Before you touch a setting
Record this first — changing settings destroys the evidence
- Whether an outdoor sensor was ever fitted
- The outdoor temperature at the time
- Any damage to the wire near the outdoor unit
- The thermostat model and its About screen
Try in this order
0 of 6 completedWhat to do first
ReversibleLook for a damaged or disconnected outdoor sensor wire.
Correct only the documented fault domain
ReversibleLennox says to compare the outdoor sensor's resistance with the temperature-resistance charts in the installation instructions and replace the sensor pack if necessary. If the sensor was removed on purpose, redo configuration and mark the sensor 'not installed' in the indoor unit's About screen to clear the alarm.
Walk the sensor wire
ReversibleFollow the wire from the outdoor unit and look for a cut, a chewed section or a loose terminal.
Compare the resistance
ReversibleLennox says to measure the sensor against the temperature-resistance charts in the installation instructions.
Replace the sensor pack or update the setting
ReversibleReplace the sensor pack if the reading is off. If it was removed on purpose, mark it not installed in the indoor unit's About screen.
Check the sensor wire at the indoor control
ReversibleWhere the outdoor sensor wire lands at the furnace or the thermostat bus, look for a loose or reversed connection; a sensor wire spliced with a wire nut and left in a wet junction is a common source of an out-of-range reading.
Model-specific
What is true of this model and not of its siblings
- Shown as
- E180 on the control or thermostat.
- Applies to
- Lennox furnaces with an outdoor air temperature sensor option.
- Clears
- 30 seconds after the fault recovers.
- Checked against
- The temperature-resistance chart in the installation instructions.
Stop boundary
When this stops being a self-service repair
- !Sensor resistance checks belong to a technician
- !Call Lennox service if the code returns after the wiring is sound
Evidence ledger
Sources behind this answer
Exact questions
Common questions
What does E180 mean on a Lennox gas furnace?+
Outdoor air temperature sensor failure. It is shown only if the sensor is shorted or out of range. It clears 30 seconds after the fault recovers.
Does E180 stop the furnace?+
It reports a sensor fault and clears 30 seconds after the fault recovers; it does not mean the furnace is locked out.
Do I need an outdoor sensor?+
Many systems run without one, but the setting must match what is fitted.
Where is the sensor?+
On the outdoor side, wired back to the indoor control.
Why does the code show only sometimes?+
Lennox lists E180 only when the sensor is shorted or out of range, so a wire that touches in wind or when wet will raise it and clear it again.
Will heating still work without the outdoor reading?+
The furnace can heat, but features that use outdoor temperature, such as balance-point and reset behavior on a heat pump pairing, work from a missing value until the sensor is fixed or marked not installed.