Lennox Error Code 13: Duplicate comfort sensor ID (Air Handler)

Updated October 13, 2026 · by Aurora Star Tech Inc.

Lennox error code 13 on a air handler means: Duplicate comfort sensor ID. It is also called Lennox diagnostic code 13.

High severityAir Handler

Homeowner? What Lennox code 13 means for you

Call a technician Your air handler is reporting: Duplicate comfort sensor ID. The air handler has locked out or cannot run properly. One reset is fine; if the code comes back, it needs a licensed technician to find the cause.

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) 657-2977 Book a service call

Licensed technicians serving Vaughan, Toronto and the GTA.

What does Lennox error code 13 mean?

The thermostat found more than one outdoor unit, indoor unit or thermostat; it shows 'Too Many Devices of the Same Type'. S30/S40 thermostat alert code 13.

Applies to: Lennox communicating air handlers and EIM-equipped indoor units in S30/S40 smart thermostat systems

Common causes of Lennox code 13

Duplicate equipment or wiring error on the communication bus

Safety: Gas, electrical and refrigerant work must be done by a licensed technician. Turn off power and gas before servicing, never bypass a safety control, and always follow the manufacturer's manual for your exact model.

Other Lennox Air Handler codes

Code	Meaning
--	Double dashes - zone sensor problem
10	Unknown device detected
11	Missing device
12	Indoor unit not detected
14	Too many devices of the same type
15	Parameter mismatch detected
20	Protocol upgrade required
21	Incompatible equipment detected
31	Lost communication with device
32	Device resetting
34	Must program unit capacity for device
35	Incorrect operation of device

All Lennox Air Handler error codes →

Lennox code 13: homeowner questions

What does Lennox code 13 mean?

Duplicate comfort sensor ID. The thermostat found more than one outdoor unit, indoor unit or thermostat; it shows 'Too Many Devices of the Same Type'. S30/S40 thermostat alert code 13.

Is it safe to keep using my air handler with code 13?

It depends on the cause. The air handler has locked out or cannot run properly. One reset is fine; if the code comes back, it needs a licensed technician to find the cause.

Can I reset Lennox code 13 myself?

You can try one reset (power off for 30 seconds, then on). If Lennox code 13 comes back, the cause is still there and a licensed technician should check it.

Who can fix Lennox code 13 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.9. 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.