Lennox Air Handler Error Codes

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

72 Lennox Air Handler error codes and diagnostic codes, with causes and troubleshooting steps for each. Select a code, or find your model below.

Homeowner with a air handler problem? Call (647) 657-2977 or book a service call — licensed technicians across Vaughan and the GTA.

Lennox Air Handler error codes list

Code	Meaning	Severity
--	Double dashes - zone sensor problem	Medium
10	Unknown device detected	High
11	Missing device	High
12	Indoor unit not detected	High
13	Duplicate comfort sensor ID	High
14	Too many devices of the same type	High
15	Parameter mismatch detected	Low
20	Protocol upgrade required	High
21	Incompatible equipment detected	High
31	Lost communication with device	High
32	Device resetting	Low
34	Must program unit capacity for device	High
35	Incorrect operation of device	High
36	Heating when not requested	High
37	Cooling when not requested	High
38	Not heating when requested	High
39	No cooling when requested	High
41	Device control board replaced	Low
500	PureAir differential pressure sensor fault	Medium
501	PureAir UV sensor fault	Medium
502	PureAir UV lamp off	Medium
503	PureAir filter life at 10%	Medium
504	PureAir filter life at 0%	Medium
505	PureAir model selection changed	Medium
506	PureAir lamp at 0% life	Medium
507	PureAir filter calibration failure	Medium
530	Zoning low damper 24 VAC	Medium
532	Zoning pressure switch opened (high pressure)	Low
542	Zone 1 temperature sensor fault	Medium
543	Zone 2 temperature sensor fault	Medium
544	Zone 3 temperature sensor fault	Medium
545	Zone 4 temperature sensor fault	Medium
546	Zone sensor parameters reset after power restore	Medium
547	Zone sensor parameters reset from system interruption	Medium
548	Zone humidity sensor error	Medium
551	Zone sensor lost communication	Medium
71511	Duct or filter blockage	Medium
71517	Indoor fan motor failure	High
E105	Wiring issue / communication problem	High
E114	AC line frequency / distortion problem	High
E115	Low secondary (24 VAC) voltage	High
E116	High secondary (24 VAC) voltage	Medium
E117	Poor ground	Medium
E120	Unresponsive device	Medium
E124	Thermostat lost communication to smart hub	High
E125	Control hardware problem	High
E126	Control internal communication problem	High
E130	Configuration jumper missing	High
E132	Device control software fault	High
E180	Outdoor temperature sensor problem	Medium
E201	Blower motor communication fault	High
E202	Blower motor and unit size mismatch	High
E203	Invalid unit size code	High
E292	Blower motor start fault	High
E295	Blower motor over temperature	Medium
E310	Discharge air temperature sensor problem	Medium
E312	Reduced airflow - indoor blower cutback	Low
E345	Relay O failure	High
E346	Heat pump jumper not removed	High
E347	Indoor or EIM relay Y1 fault	High
E348	Indoor relay Y2 fault	Medium
E350	Electric heat not configured	High
E351	Electric heat stage 1 fault	High
E352	Electric heat stage 2 fault	Medium
E353	Electric heat stage 3 fault	Medium
E354	Electric heat stage 4 fault	Medium
E355	Electric heat stage 5 fault	Medium
E371	Float switch sensed open	High
E380	EIM interlock relay fault	High
E381	EIM interlock relay stuck	High
E382	EIM relay W1 fault	High
E420	EIM defrost out of cycle	Medium

Air Handler troubleshooting guides

Two horizontal lines on display (soft disable) - Lennox communicating Lennox · Air Handler

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.

Lennox Air Handler error codes list

Air Handler troubleshooting guides

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