AC Error Codes · Lennox
Lennox AC Error Codes: Four Separate Code Systems Explained
Find your code, understand what it means, then run a guided diagnosis.
Error Code Finder
Look a code up against sourced manufacturer records. Codes we cannot source are not listed — a guessed meaning is worse than no meaning.
Lennox is the widest code spread of any brand in our database: four genuinely different architectures across its product lines. Mini-splits use two-part prefix codes such as EH 60 and PC 08. Older splits and ducted units use a large E/F/H/P/U/L alphanumeric table. Residential communicating systems report plain numbers from 105 to 417. Rooftop and packaged units use their own three-digit set entirely. Identifying which system you are reading is the first diagnostic step.
How do Lennox AC error codes work?
It depends on the product line. Mini-splits use prefix codes: EH for indoor faults, EL for communication and leak detection, EC for outdoor faults and PC for outdoor protections. Legacy splits and ducted units use an E/F/H/P/U/L alphanumeric table. Residential communicating systems use numeric alerts — 105 to 180 for network and control faults, 400 to 417 for compressor and pressure faults. Rooftop units use a separate three-digit table.
Product families covered
-
Mini-split (prefix codes)
EH / EL / EC / PC two-part codes from the official service manual.
-
Legacy split / ducted (alphanumeric)
A large E/F/H/P/U/L table structurally similar to Gree, TOSOT and Midea.
-
Communicating residential (numeric alerts)
105–417 alerts from the thermostat/board network.
-
Rooftop / packaged (LF20)
A separate commercial three-digit code table.
Where the code is displayed — and why it matters
The same fault can be labelled differently depending on which display you read it from, so identify the display before looking the code up.
- Mini-split indoor display
- Shows the EH / EL / PC style code.
- Mini-split outdoor LEDs
- Uses its own numbering for the same event — the outdoor LED may show F4 while the indoor shows E2 for the same communication fault.
- Communicating thermostat
- Shows numeric alert codes for the whole system network.
- Rooftop controller (Climatic)
- Shows the three-digit rooftop fault set.
Lennox code formats at a glance
The format identifies the system before you look the code up:
- EH / EL / EC / PC + pair
- Mini-split: indoor, communication/leak, outdoor, outdoor protection
- E / F / H / P / U / L + digit
- Legacy split and ducted alphanumeric table
- 3-digit 105–417
- Residential communicating system alerts
- 3-digit 000–147
- Rooftop / packaged unit faults
How the families differ
- Indoor and outdoor mini-split displays use separate numbering for the same fault event, so both readings should be recorded and cross-referenced rather than assumed identical.
- The legacy alphanumeric table is structurally similar to Gree, TOSOT and Midea tables, which points to a shared OEM inverter-control platform in some ranges — useful context, but codes must still be read against Lennox documentation.
- The communicating numeric alerts are network and controls faults, closer in nature to Trane's communicating codes than to a simple split-AC fault table.
- Rooftop and packaged codes belong to the commercial branch and must never be read against residential split tables.
Lennox mini-split codes (official service manual)
From the official Lennox mini-split user guide and service manual. Severity is not given per code in our Lennox source material, so no severity level is published.
| Code | What it reports | Applies to | Severity | Source |
|---|---|---|---|---|
| EH 00 | Indicates indoor unit EEPROM error | Mini-split (prefix codes) | — | B |
| EH 0A | Indicates indoor unit EEPROM parameter error | Mini-split (prefix codes) | — | B |
| EL 01 | Indicates communication error between indoor unit and outdoor units | Mini-split (prefix codes) | — | B |
| EH 03 | Indicates indoor fan speed error (DC motor) | Mini-split (prefix codes) | — | B |
| EH 60 | Indicates indoor room temperature sensor error (T1) | Mini-split (prefix codes) | — | B |
| EH 61 | Indicates indoor coil temperature sensor error (T2) | Mini-split (prefix codes) | — | B |
| EL 0C | Indicates refrigerant leakage detection (cooling mode only) | Mini-split (prefix codes) | — | B |
| EH 0b | Indicates communication error between main control board and display board | Mini-split (prefix codes) | — | B |
| EC 51 | Indicates outdoor unit EEPROM error | Mini-split (prefix codes) | — | B |
| EC 52 | Indicates outdoor coil temperature sensor error (T3) | Mini-split (prefix codes) | — | B |
| EC 53 | Indicates outdoor ambient temperature sensor error (T4) | Mini-split (prefix codes) | — | B |
| EC 54 | Indicates compressor discharge temperature sensor error (T5) | Mini-split (prefix codes) | — | B |
| EC 07 | Indicates outdoor unit fan speed error (DC fan motor) | Mini-split (prefix codes) | — | B |
| PC 00 | Indicates inverter module IPM error | Mini-split (prefix codes) | — | B |
| PC 01 | Indicates high or low voltage protection | Mini-split (prefix codes) | — | B |
| PC 04 | Indicates compressor drive error | Mini-split (prefix codes) | — | B |
| PC 08 | Indicates outdoor current overload protection | Mini-split (prefix codes) | — | B |
| PC 0L | Indicates outdoor low ambient temperature protection | Mini-split (prefix codes) | — | B |
Lennox legacy split / ducted alphanumeric codes
A cross-validated compilation. Several E codes are documented with two different meanings across product lines — both are published and flagged rather than resolved.
| Code | What it reports | Applies to | Severity | Source |
|---|---|---|---|---|
| E0 | Is reported to indicate eEPROM parameter error | Legacy split / ducted (alphanumeric) | — | C |
| E1 | Is reported to indicate indoor/outdoor communication protection, or high-pressure protection Our Lennox legacy-table source records two different documented meanings for this code across Lennox product lines. Both are published; the model's own service documentation resolves which applies. | Legacy split / ducted (alphanumeric) | — | C |
| E2 | Is reported to indicate zero-crossing signal error, or anti-freezing protection Our Lennox legacy-table source records two different documented meanings for this code across Lennox product lines. Both are published; the model's own service documentation resolves which applies. | Legacy split / ducted (alphanumeric) | — | C |
| E3 | Is reported to indicate indoor fan speed out of control, or low-pressure protection Our Lennox legacy-table source records two different documented meanings for this code across Lennox product lines. Both are published; the model's own service documentation resolves which applies. | Legacy split / ducted (alphanumeric) | — | C |
| E4 | Is reported to indicate high discharge temperature protection | Legacy split / ducted (alphanumeric) | — | C |
| E5 | Is reported to indicate outdoor temperature sensor open/short or EEPROM error, or whole-unit overcurrent protection Our Lennox legacy-table source records two different documented meanings for this code across Lennox product lines. Both are published; the model's own service documentation resolves which applies. | Legacy split / ducted (alphanumeric) | — | C |
| E6 | Is reported to indicate room or evaporator sensor open/short circuit, or indoor–outdoor communication error Our Lennox legacy-table source records two different documented meanings for this code across Lennox product lines. Both are published; the model's own service documentation resolves which applies. | Legacy split / ducted (alphanumeric) | — | C |
| E7 | Is reported to indicate outdoor fan speed out of control, or running mode conflict Our Lennox legacy-table source records two different documented meanings for this code across Lennox product lines. Both are published; the model's own service documentation resolves which applies. | Legacy split / ducted (alphanumeric) | — | C |
| E8 | Is reported to indicate overload protection | Legacy split / ducted (alphanumeric) | — | C |
| E9 | Is reported to indicate indoor unit full-water error | Legacy split / ducted (alphanumeric) | — | C |
| EN | Is reported to indicate current protection | Legacy split / ducted (alphanumeric) | — | C |
| EU | Is reported to indicate frequency reduced by IPM temperature protection | Legacy split / ducted (alphanumeric) | — | C |
| F0 | Is reported to indicate system refrigerant shortage or blockage protection | Legacy split / ducted (alphanumeric) | — | C |
| F1 | Is reported to indicate return air temperature sensor open/short circuit | Legacy split / ducted (alphanumeric) | — | C |
| F2 | Is reported to indicate evaporator temperature sensor open/short circuit | Legacy split / ducted (alphanumeric) | — | C |
| F3 | Is reported to indicate outdoor ambient temperature sensor open/short circuit | Legacy split / ducted (alphanumeric) | — | C |
| F4 | Is reported to indicate outdoor condenser mid-tube temperature sensor open/short circuit | Legacy split / ducted (alphanumeric) | — | C |
| F5 | Is reported to indicate discharge temperature sensor open/short circuit | Legacy split / ducted (alphanumeric) | — | C |
| F6 | Is reported to indicate frequency reduced by overload protection | Legacy split / ducted (alphanumeric) | — | C |
| F8 | Is reported to indicate frequency reduced by whole-unit current protection | Legacy split / ducted (alphanumeric) | — | C |
| F9 | Is reported to indicate frequency reduced by high discharge temperature | Legacy split / ducted (alphanumeric) | — | C |
| FH | Is reported to indicate frequency reduced by anti-freezing protection | Legacy split / ducted (alphanumeric) | — | C |
| Fo | Is reported to indicate pump-down in progress | Legacy split / ducted (alphanumeric) | — | C |
| H1 | Is reported to indicate forced defrosting | Legacy split / ducted (alphanumeric) | — | C |
| H3 | Is reported to indicate compressor overheating protection | Legacy split / ducted (alphanumeric) | — | C |
| H5 | Is reported to indicate iPM current protection | Legacy split / ducted (alphanumeric) | — | C |
| H6 | Is reported to indicate motor stalling | Legacy split / ducted (alphanumeric) | — | C |
| H7 | Is reported to indicate compressor desynchronizing | Legacy split / ducted (alphanumeric) | — | C |
| HC | Is reported to indicate pFC protection | Legacy split / ducted (alphanumeric) | — | C |
| HE | Is reported to indicate compressor demagnetization protection | Legacy split / ducted (alphanumeric) | — | C |
| P0 | Is reported to indicate iPM malfunction / IGBT over-current protection | Legacy split / ducted (alphanumeric) | — | C |
| P1 | Is reported to indicate over-voltage or under-voltage protection | Legacy split / ducted (alphanumeric) | — | C |
| P2 | Is reported to indicate compressor top temperature protection | Legacy split / ducted (alphanumeric) | — | C |
| P4 | Is reported to indicate inverter compressor drive error | Legacy split / ducted (alphanumeric) | — | C |
| P5 | Is reported to indicate over phase current protection | Legacy split / ducted (alphanumeric) | — | C |
| P6 | Is reported to indicate drive board communication error | Legacy split / ducted (alphanumeric) | — | C |
| P7 | Is reported to indicate iPM temperature sensor open/short circuit | Legacy split / ducted (alphanumeric) | — | C |
| P8 | Is reported to indicate iPM temperature protection | Legacy split / ducted (alphanumeric) | — | C |
| P9 | Is reported to indicate aC contactor protection | Legacy split / ducted (alphanumeric) | — | C |
| PD | Is reported to indicate sensor connection protection | Legacy split / ducted (alphanumeric) | — | C |
| PE | Is reported to indicate temperature drift protection | Legacy split / ducted (alphanumeric) | — | C |
| PF | Is reported to indicate drive board temperature sensor error | Legacy split / ducted (alphanumeric) | — | C |
| PH | Is reported to indicate dC bus over-voltage protection | Legacy split / ducted (alphanumeric) | — | C |
| PL | Is reported to indicate dC bus under-voltage protection | Legacy split / ducted (alphanumeric) | — | C |
| PP | Is reported to indicate aC input voltage abnormal | Legacy split / ducted (alphanumeric) | — | C |
| PU | Is reported to indicate capacitor charging error | Legacy split / ducted (alphanumeric) | — | C |
| U1 | Is reported to indicate compressor phase current sensing circuit error | Legacy split / ducted (alphanumeric) | — | C |
| U3 | Is reported to indicate dC bus voltage drop error | Legacy split / ducted (alphanumeric) | — | C |
| U5 | Is reported to indicate whole-unit current sensing circuit error | Legacy split / ducted (alphanumeric) | — | C |
| U7 | Is reported to indicate four-way valve reversing error | Legacy split / ducted (alphanumeric) | — | C |
| U8 | Is reported to indicate pG motor zero-crossing protection | Legacy split / ducted (alphanumeric) | — | C |
| L3 | Is reported to indicate outdoor fan 1 error protection | Legacy split / ducted (alphanumeric) | — | C |
| L9 | Is reported to indicate over-power protection | Legacy split / ducted (alphanumeric) | — | C |
| LA | Is reported to indicate outdoor fan 2 error protection | Legacy split / ducted (alphanumeric) | — | C |
| LC | Is reported to indicate compressor startup failure | Legacy split / ducted (alphanumeric) | — | C |
| Ld | Is reported to indicate compressor phase loss or reversal protection | Legacy split / ducted (alphanumeric) | — | C |
| LE | Is reported to indicate compressor stalling | Legacy split / ducted (alphanumeric) | — | C |
| LF | Is reported to indicate over-speeding | Legacy split / ducted (alphanumeric) | — | C |
| LP | Is reported to indicate indoor and outdoor units unmatched | Legacy split / ducted (alphanumeric) | — | C |
| B5 | Is reported to indicate indoor liquid-valve temperature sensor open/short circuit | Legacy split / ducted (alphanumeric) | — | C |
| B7 | Is reported to indicate indoor gas-valve temperature sensor open/short circuit | Legacy split / ducted (alphanumeric) | — | C |
| C5 | Is reported to indicate jumper error | Legacy split / ducted (alphanumeric) | — | C |
| DN | Is reported to indicate communication line misconnected, or expansion valve error Our Lennox legacy-table source records two different documented meanings for this code across Lennox product lines. Both are published; the model's own service documentation resolves which applies. | Legacy split / ducted (alphanumeric) | — | C |
Lennox communicating residential alert codes
From the official Lennox residential communicating systems alert code guide. These are network and controls alerts, not split-AC fault codes.
| Code | What it reports | Applies to | Severity | Source |
|---|---|---|---|---|
| 105 | Indicates device communication failure | Communicating residential (numeric alerts) | — | B |
| 120 | Indicates unresponsive device | Communicating residential (numeric alerts) | — | B |
| 124 | Indicates active subnet controller missing | Communicating residential (numeric alerts) | — | B |
| 125 | Indicates hardware failure | Communicating residential (numeric alerts) | — | B |
| 126 | Indicates internal control communication failure | Communicating residential (numeric alerts) | — | B |
| 131 | Indicates corrupted control parameters | Communicating residential (numeric alerts) | — | B |
| 132 | Indicates failed flash CRC check | Communicating residential (numeric alerts) | — | B |
| 180 | Indicates ambient sensor problem | Communicating residential (numeric alerts) | — | B |
| 400 | Indicates compressor internal overload trip | Communicating residential (numeric alerts) | — | B |
| 401 | Indicates long run time — extremely long compressor run cycles | Communicating residential (numeric alerts) | — | B |
| 402 | Indicates system pressure trip | Communicating residential (numeric alerts) | — | B |
| 403 | Indicates short cycling — compressor running under 3 minutes per cycle | Communicating residential (numeric alerts) | — | B |
| 404 | Indicates locked rotor — run capacitor short, seized bearings, or excessive liquid refrigerant | Communicating residential (numeric alerts) | — | B |
| 405 | Indicates open circuit | Communicating residential (numeric alerts) | — | B |
| 406 | Indicates open start circuit | Communicating residential (numeric alerts) | — | B |
| 407 | Indicates open run circuit | Communicating residential (numeric alerts) | — | B |
| 408 | Indicates welded contactor — compressor always runs | Communicating residential (numeric alerts) | — | B |
| 409 | Indicates secondary low voltage | Communicating residential (numeric alerts) | — | B |
| 410 | Indicates low-pressure fault | Communicating residential (numeric alerts) | — | B |
| 411 | Indicates low-pressure switch lockout | Communicating residential (numeric alerts) | — | B |
| 412 | Indicates high-pressure fault | Communicating residential (numeric alerts) | — | B |
| 413 | Indicates high-pressure switch lockout | Communicating residential (numeric alerts) | — | B |
| 414 | Indicates discharge line temperature fault | Communicating residential (numeric alerts) | — | B |
| 415 | Indicates discharge line temperature lockout | Communicating residential (numeric alerts) | — | B |
| 417 | Indicates discharge sensor fault | Communicating residential (numeric alerts) | — | B |
Lennox rooftop / packaged (LF20) faults
From the official Lennox Climatic 2 LF20 rooftop codes-and-faults document. File these with commercial rooftop diagnostics.
| Code | What it reports | Applies to | Severity | Source |
|---|---|---|---|---|
| 000 | Indicates no fault | Rooftop / packaged (LF20) | — | B |
| 001 | Indicates airflow failure | Rooftop / packaged (LF20) | — | B |
| 004 | Indicates dirty filters | Rooftop / packaged (LF20) | — | B |
| 005 | Indicates missing filters | Rooftop / packaged (LF20) | — | B |
| 011 | Indicates faulty electrical heater batteries | Rooftop / packaged (LF20) | — | B |
| 012 | Indicates supply air over-temperature | Rooftop / packaged (LF20) | — | B |
| 013 | Indicates room temperature too low | Rooftop / packaged (LF20) | — | B |
| 022 | Indicates supply temperature too low | Rooftop / packaged (LF20) | — | B |
| 023 | Indicates room over-temperature | Rooftop / packaged (LF20) | — | B |
| 031 | Indicates faulty humidifier | Rooftop / packaged (LF20) | — | B |
| 032 | Indicates room humidity too low | Rooftop / packaged (LF20) | — | B |
| 033 | Indicates room over-humidity | Rooftop / packaged (LF20) | — | B |
| 041 | Indicates faulty pump | Rooftop / packaged (LF20) | — | B |
| 081 | Indicates faulty return air / room temperature sensor | Rooftop / packaged (LF20) | — | B |
| 082 | Indicates faulty return air / room relative humidity sensor | Rooftop / packaged (LF20) | — | B |
| 083 | Indicates faulty outside temperature sensor | Rooftop / packaged (LF20) | — | B |
| 091 | Indicates faulty blower fan | Rooftop / packaged (LF20) | — | B |
| 092–095 | Indicates faulty condenser, systems 1–4 | Rooftop / packaged (LF20) | — | B |
| 096 | Indicates condenser water temperature too low | Rooftop / packaged (LF20) | — | B |
| 097 | Indicates condenser water over-temperature | Rooftop / packaged (LF20) | — | B |
| 111 | Indicates faulty condenser temperature sensor, compressor no. 1 | Rooftop / packaged (LF20) | — | B |
| 142 | Indicates faulty pressure transmitter, compressor no. 4 | Rooftop / packaged (LF20) | — | B |
| 145 | Indicates faulty high pressure or electrical power fault, compressor no. 4 | Rooftop / packaged (LF20) | — | B |
| 147 | Indicates faulty low pressure, compressor no. 4 | Rooftop / packaged (LF20) | — | B |
Before you act on a code
- Read the code against the right system — a legacy E2 and a mini-split EH-prefixed code are different architectures with different meanings.
- PC and P-series codes are inverter and supply protections: leave the unit off rather than power-cycling repeatedly.
- Codes marked as conflicting have two documented meanings across Lennox lines. We publish both; only your model's service documentation resolves them.
- Lennox VRF-equivalent commercial codes, if any exist, were not surfaced in our research and are not published here.
Corroborated across independent technical sources
How to identify your system
- Note the exact code and its format — a two-part prefix code, a letter-plus-digit code, or a plain three-digit number.
- Note where you read it: indoor display, outdoor LEDs, a communicating thermostat, or a rooftop controller.
- For mini-splits, record both the indoor and outdoor readings if both are visible.
No code showing? Start from the symptom
Lennox error codes — common questions
Why does my Lennox outdoor unit show a different code from the indoor display?
Because Lennox mini-split indoor and outdoor displays use separate numbering conventions for the same fault event — the outdoor LEDs can show F4 while the indoor display shows E2 for a communication malfunction. Both readings describe one fault and should be cross-referenced, not treated as two problems.
What does Lennox EL 01 mean?
EL 01 is a communication error between the indoor and outdoor unit on a mini-split. The cooling circuit may be healthy; the fault sits in the interconnecting wiring, the terminations or the boards at either end.
What does Lennox alert 403 mean?
403 reports short cycling — the compressor is running under three minutes per cycle. That points at controls, refrigerant charge or load rather than a single failed part, and repeated short cycling shortens compressor life.
Is Lennox H1 a fault?
No. On the legacy alphanumeric table H1 indicates forced defrosting, which is normal operation. If the unit is not cooling while H1 is displayed, let the cycle complete before treating it as a breakdown.
Need this looked at properly?
Call or send a photo on WhatsApp and we will tell you whether it needs an inspection, and what the work involves, before anyone travels.
Sources consulted
- Official Lennox mini-split user guide and service manual (indoor display / outdoor LED tables)
- Official Lennox residential communicating systems alert code guide
- Official Lennox Climatic 2 LF20 rooftop codes-and-faults document
- Cross-validated independent Lennox compilation (legacy alphanumeric table)