On the covered Lennox gas furnace, E310 means discharge temperature sensor failure, shown only if the sensor is shorted or out of range. In communicating mode it clears 30 seconds after the fault recovers; in non-communicating mode it clears after the current heat call. First, look for a damaged or disconnected sensor wire.
Differential
Likely causes of “Lennox gas furnace code E310”, and how to tell them apart
- 1
A shorted or out-of-range discharge temperature sensor
What separates it E310 shows
How to confirm Lennox says to compare its resistance with the chart
- 2
A damaged or disconnected sensor wire
What separates it The code appears after work
How to confirm Look for a loose or damaged wire
- 3
A failed sensor
What separates it The reading never changes
How to confirm Replace the sensor if necessary
- 4
A control fault
What separates it The sensor tests well
How to confirm Technician replacement
- 5
A recovered fault
What separates it The code clears after the fault recovers
How to confirm Watch the next cycles
Before you touch a setting
Record this first — changing settings destroys the evidence
- Whether the furnace is communicating with the thermostat
- How the code clears after a call for heat
- Any signs of damaged wire near the sensor
- The furnace model from the label
Try in this order
0 of 8 completedWhat to do first
ReversibleLook for a damaged or disconnected sensor wire.
Correct only the documented fault domain
ReversibleLennox says to compare the sensor's resistance with the temperature-resistance charts in the installation instructions and replace the sensor if necessary.
Turn the power off
ReversibleAt the switch.
Look for a damaged wire
ReversibleNear the sensor, without touching.
Restart
ReversibleAnd watch the display.
Note whether it clears
ReversibleLennox says 30 seconds after recovery in communicating mode.
Record the pattern
ReversibleAnd time.
Call a technician
ReversibleTo test the sensor.
Model-specific
What is true of this model and not of its siblings
- The discharge sensor
- The sensor measures the temperature of the air leaving the furnace, which the control uses to modulate the heat.
- Lennox's wording
- Shown only if the sensor is shorted or out of range.
- Communicating and non-communicating
- In communicating mode it clears 30 seconds after recovery; in non-communicating mode it clears after the current heat call.
- The test
- Lennox says to compare resistance with the temperature-resistance charts.
- The wire
- Look for a damaged wire, without touching.
- Replacement
- If the sensor is bad, replace it.
- What a sensor reading means
- A thermistor changes its electrical resistance with temperature. The control reads the resistance and converts it to a temperature. If the reading is zero, as in a short, or infinite, as in a break, it is out of range, and the control reports E310.
- A short or a break
- A wire rubbed through by vibration can short, and a wire pulled out of its connector can break. Both look alike to the control. A technician inspects the harness and the connector pins, with the power off.
- Clearing the code
- Lennox says that in communicating mode the code clears 30 seconds after the fault recovers, and in non-communicating mode it clears after the current heat call. If it clears and returns, the connection is likely intermittent, which a careful inspection often finds.
Stop boundary
When this stops being a self-service repair
- !Do not touch electrical parts with the power on
- !Call a qualified technician for a sensor test
- !Never bypass a sensor
- !Sensor work is for a technician
- !Contact Lennox service if the reading stays out of range after wiring is checked
Evidence ledger
Sources behind this answer
Exact questions
Common questions
What does E310 mean on a Lennox gas furnace?+
Discharge temperature sensor failure, shown only if the sensor is shorted or out of range. In communicating mode it clears 30 seconds after the fault recovers; in non-communicating mode it clears after the current heat call.
When does it clear?+
In communicating mode, 30 seconds after the fault recovers.
Is the furnace safe to use?+
Follow the technician's advice.
How is it tested?+
By resistance against a chart.
Where is the discharge sensor?+
In the supply airstream after the heat exchanger, wired back to the control.
Can a bad sensor overheat the furnace?+
The limit switches still guard the heat exchanger; the sensor is used for control.