Lennox Error Code E120: Unresponsive device (Air Handler)
Lennox error code E120 on a air handler means: Unresponsive device. It is also called Lennox diagnostic code E120.
Homeowner? What Lennox code E120 means for you
Check, then call Your air handler is reporting: Unresponsive device. This is often caused by something simple. Try the safe checks below; if the code returns, book a service call before it turns into a no-heat or no-hot-water emergency.
Safe things you can check yourself
- Check the thermostat: right mode (Heat or Cool), set a few degrees past room temperature, and fresh batteries if it uses them.
- Make sure the unit has power: its on/off switch (often looks like a light switch near the unit) is ON and the breaker in the electrical panel is not tripped.
- Look at the air filter. If it is grey and clogged, replace it; a blocked filter causes many shutdowns.
- Try one reset: turn the power off for 30 seconds, then back on. If the code comes back, stop resetting and call a technician.
Call (647) 657-2977Book a service call
Licensed technicians serving Vaughan, Toronto and the GTA.
What does Lennox error code E120 mean?
A component is slow to respond to the system, usually the outdoor unit answering the thermostat; often harmless and clears by itself. S30/S40 thermostat alert code 120 (shown as E120 on the unit control display).
Applies to: Lennox communicating air handlers and EIM-equipped indoor units in S30/S40 smart thermostat systems
Common causes of Lennox code E120
- Slow outdoor unit response
- Voltage leaking between strands in the cable bundle
Other Lennox Air Handler codes
All Lennox Air Handler error codes →
Lennox code E120: homeowner questions
What does Lennox code E120 mean?
Unresponsive device. A component is slow to respond to the system, usually the outdoor unit answering the thermostat; often harmless and clears by itself. S30/S40 thermostat alert code 120 (shown as E120 on the unit control display).
Is it safe to keep using my air handler with code E120?
It depends on the cause. This is often caused by something simple. Try the safe checks below; if the code returns, book a service call before it turns into a no-heat or no-hot-water emergency.
Can I reset Lennox code E120 myself?
You can try one reset (power off for 30 seconds, then on). If Lennox code E120 comes back, the cause is still there and a licensed technician should check it.
Who can fix Lennox code E120 near me?
Aurora Star Tech Inc. repairs Lennox air handlers in Vaughan, Toronto and across the GTA. Call (647) 657-2977 or book a service call online.
Troubleshooting guides
- Two horizontal lines on display (soft disable) - Lennox communicating Lennox · Air Handler
Source: Lennox Residential Communicating Systems Alert Code Guide (V2) 100017 (3/2023), Table 2 Alert Codes and Troubleshooting, p.17. Written in our own words as a summary; always check the original manual.
General guidance for qualified technicians. The manufacturer's installation and service manual and local codes always take priority. Aurora Star Tech is not affiliated with, endorsed by or sponsored by any equipment manufacturer; brand and model names are used only to identify equipment and belong to their owners.