HVACopediaLennox air handler error codes
72 codes with causes and test steps.
| Code | Meaning | Severity |
|---|---|---|
| 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 |
| -- | Double dashes - zone sensor problem | Medium |
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.