The LG Air Conditioner CH05 error code means the indoor and outdoor units are not communicating correctly. One common reason is that the outdoor unit has lost power because its circuit breaker has tripped, even though the indoor unit still turns on.
Start by checking the breakers for both units. When it is safe to do so, switch off power to the complete air-conditioning system, wait about five minutes, and restore power to both units together. LG recommends arranging service when CH05 remains after this reset.
Do not repeatedly reset a breaker that trips again. Stop using the system immediately if you notice a burning smell, damaged cable, buzzing, smoke, excessive heat, or signs of water near electrical components.
Air Conditioner CH05 Error Code
| Item | Details |
|---|---|
| Error code | CH05, sometimes displayed as CH 05 |
| Meaning | Communication failure between the indoor and outdoor units |
| Appliance | LG split, multi-split or system air conditioner |
| Most common homeowner-level cause | Outdoor unit has lost power or its breaker has tripped |
| Safe first check | Confirm that both indoor and outdoor unit breakers are on |
| Basic reset | Switch off both units for 3–5 minutes, then restore power together |
| Can the air conditioner still be used? | Not normally while the fault is active |
| Repair difficulty | Easy only when caused by a one-time power interruption; otherwise professional |
| Call a technician when | The code returns, the breaker trips again, or the system was recently installed or repaired |
What does CH05 mean on an LG air conditioner?
CH05 indicates an abnormal communication condition between the indoor unit and the outdoor unit. The indoor section may still have power and respond to the remote, but it cannot exchange the required operating signals with the outdoor section.
This is primarily an electrical power, communication wiring or control-system fault. It does not directly identify:
- A dirty air filter
- Low refrigerant
- A blocked drain
- A damaged compressor
- An incorrect temperature setting
Those problems may affect cooling, but they are not the normal direct meaning of CH05.
The system may show the code shortly after startup because the indoor controller checks whether it can communicate with the outdoor controller before normal cooling or heating continues.
Common causes of the LG CH05 error
| Possible cause | What may be happening | Who should check it? |
|---|---|---|
| Outdoor unit breaker is tripped | The indoor unit has power, but the outdoor unit is unavailable | Homeowner may check the breaker |
| Temporary power interruption | One section may have restarted before the other | Homeowner may perform one safe reset |
| Incorrect installation wiring | Indoor and outdoor terminal connections may not match | Qualified installer or HVAC technician |
| Loose or damaged interconnecting cable | Communication signals cannot travel reliably between units | Qualified technician |
| Poor terminal connection | A loose, overheated or corroded terminal interrupts power or communication | Qualified technician |
| Indoor control board fault | The indoor PCB may not send or receive data correctly | Qualified technician |
| Outdoor control board fault | The outdoor PCB or its power supply may not operate | Qualified technician |
| Electrical supply problem | Incorrect voltage, damaged isolation equipment or another circuit fault may interrupt operation | Licensed electrician or HVAC technician |
LG specifically identifies a tripped outdoor-unit breaker as a cause of CH05. Its installation documentation also warns that incorrectly matched indoor-to-outdoor wires can produce CH05 or CH53.
Safe checks you can perform
1. Confirm the displayed code
Make sure the display reads CH05, not CH03, CH35, CH53 or another similar code.
Some LG products show the code on:
- The indoor unit display
- A wired wall controller
- A remote controller
- Flashing indicator lights
The display method varies by product family, so check the user manual for your exact model if the code is being shown through LED flashes.
2. Check whether both units have power
An LG split system contains an indoor unit and an outdoor unit. Depending on the installation, they may use:
- One shared air-conditioner circuit
- Separate indoor and outdoor breakers
- A main breaker plus an outdoor isolation switch
Look at the electrical panel without removing any covers. Check whether a breaker marked air conditioner, AC, heat pump, indoor unit or outdoor unit has moved to the tripped position.
A tripped breaker may sit between the fully on and fully off positions.
3. Reset a tripped breaker once
Only attempt this when:
- There is no burning smell
- There is no visible cable damage
- There is no smoke or unusual heat
- Water has not entered the electrical equipment
- The breaker has not been repeatedly tripping
Move the affected breaker fully to off, then follow the complete reset procedure below.
Do not continue resetting it if it trips again. LG advises professional inspection when the outdoor breaker will not stay on.
4. Note when the error started
This information can help a technician find the cause faster. Record whether CH05 appeared:
- After a power outage
- After an electrical storm
- Immediately after installation
- After the air conditioner was serviced
- After building or renovation work
- Only during very hot or wet weather
- Intermittently rather than on every startup
A fault that begins immediately after installation or cable work makes an incorrect or loose connection more likely than a random control-board failure.
How to reset an LG air conditioner with CH05
LG reset instructions vary slightly between support pages. One official guide specifies five minutes, while another system-air-conditioner guide specifies three minutes. Following a five-minute wait is appropriate unless the manual for your exact model gives a different procedure.
Reset procedure
- Turn the air conditioner off with its controller or remote.
- Locate the breakers supplying the indoor and outdoor units.
- Switch off the outdoor-unit breaker.
- Switch off the indoor-unit breaker as well. When the installation uses one shared circuit, switch off that single air-conditioner breaker.
- Wait five full minutes.
- Restore power to both sections together. Where separate breakers are fitted, turn them on at approximately the same time.
- Wait several minutes for the system to initialise.
- Select cooling or heating and check whether CH05 returns.
A power reset may clear a temporary startup or communication interruption. It will not repair crossed wires, damaged cables, loose terminals or faulty circuit boards.
When the reset works
The air conditioner may be used cautiously when:
- CH05 disappears
- Both units start normally
- The outdoor unit remains powered
- The breaker does not trip again
- There is no unusual smell, sound or heat
Monitor the system during the next several operating cycles. Arrange service if the code returns, even if another reset clears it temporarily.
What to do when CH05 returns after resetting
A returning code usually means the communication problem is still present. Repeatedly cutting and restoring power is unlikely to solve a physical wiring or control-board fault.
At this stage, stop homeowner troubleshooting and arrange an inspection. LG states that service is required when CH05 persists after the power and breaker check.
A technician may need to check:
- Power reaching the outdoor unit
- Indoor and outdoor terminal positions
- The condition of the interconnecting cable
- Loose, corroded or overheated terminals
- Grounding and electrical supply condition
- Communication signals between controllers
- Indoor control-board operation
- Outdoor control-board and power-supply operation
These checks can involve mains electricity and live electrical measurements. They should not be attempted by an untrained homeowner.
CH05 immediately after installation or repair
A CH05 code that appears from the first startup often points to an installation or connection problem.
LG’s installation guide shows that indoor and outdoor terminals must be correctly matched. It directly associates mismatched wiring with CH05 and CH53. The same guide warns that wrong or loose electrical connections can create overheating and fire hazards.
Contact the installer when the error began after:
- A new air conditioner installation
- Replacement of an indoor or outdoor unit
- Control-board replacement
- Electrical rewiring
- Relocation of the system
- Work around the interconnecting cable
Do not open the terminal covers to compare wires yourself. Photograph the displayed code and provide the installer with the indoor and outdoor model numbers.
Why CH05 may appear after a power cut
After a power outage, one part of the system may receive power while another breaker remains tripped or an outdoor isolation switch stays off. The indoor unit then attempts to communicate with an outdoor unit that is unavailable.
A coordinated reset of both sections may restore communication. This is an inference from LG’s breaker and reset instructions rather than proof of the exact cause in every outage-related case.
Service is needed when:
- CH05 appears after every outage
- The outdoor breaker repeatedly trips
- The error returns once cooling begins
- The system works only after several resets
Possible faulty parts
CH05 does not identify one specific failed component. The code identifies the lost communication, while further testing is required to locate the cause.
| Component or area | How it may relate to CH05 | Repair level |
|---|---|---|
| Outdoor circuit breaker or isolator | May prevent power from reaching the outdoor unit | Electrician or HVAC technician if defective |
| Interconnecting cable | May be damaged, disconnected or incorrectly terminated | Professional |
| Terminal block or connector | May be loose, corroded or overheated | Professional |
| Indoor PCB | May fail to send or receive communication data | Professional |
| Outdoor main PCB | May be unpowered or unable to communicate | Professional |
| Outdoor power-supply circuit | May prevent the control electronics from starting | Professional |
A technician should diagnose the fault before any board or cable is replaced. Replacing parts based only on the CH05 display may not solve the underlying problem.
Model and regional differences
CH05 appears across several LG inverter and system air-conditioning families, including residential split systems and commercial Multi V equipment. However, the precise diagnostic definition and testing sequence can vary by series. LG publishes a separate Multi V troubleshooting resource covering CH05, CH53 and CH237.
Official LG error-code guides in some regions group CH05, E0 and CH53 as indoor-to-outdoor communication errors. This does not mean the codes are interchangeable on every model. Use the manual for the exact indoor and outdoor unit combination.
Regional differences can include:
- Three-minute or five-minute reset waiting periods
- One shared breaker or separate breakers
- CH05 shown as text or flashing LEDs
- Different code definitions on residential and commercial systems
- Different service contacts and warranty procedures
The electrical voltage used in the country does not change the basic CH05 meaning, but it does change how the supply must be tested. Do not use voltage values or wiring diagrams from another regional model.
Can you continue using the air conditioner?
The system will often limit or stop operation while CH05 is active because the indoor and outdoor controllers cannot coordinate safely.
One reset is reasonable when the fault followed a brief power interruption and the breaker remains stable. Do not continue operating or resetting the system when:
- The breaker trips again
- CH05 repeatedly returns
- The outdoor unit does not start
- The system makes clicking or buzzing sounds
- A cable or isolator appears damaged
- You smell burning or hot plastic
- The fault began after installation work
The outdoor fan spinning does not prove that communication is normal. Some outdoor components may receive power even when the required control signal is missing.
When to call an HVAC technician
Arrange professional service when any of these conditions apply:
- CH05 remains after one correct reset
- The breaker will not stay on
- The error returns repeatedly
- The air conditioner was recently installed or rewired
- Only one indoor unit in a multi-split system shows the fault
- Several indoor units display communication codes
- There is visible cable, isolator or weather damage
- The indoor unit runs but the outdoor unit does not
- There is a smell of burning, smoke or unusual electrical noise
For a newly installed system, contact the original installer first. For an in-warranty unit, use the authorised service route for your country before approving third-party repairs.
Safety warning
Do not remove indoor or outdoor electrical covers, touch terminals, bypass breakers, test live voltage or replace control boards yourself.
LG’s installation documentation warns that incorrect and loose wiring can cause heat and fire. Internal diagnosis should be completed by a qualified HVAC technician or licensed electrician familiar with the local electrical rules.
Frequently asked questions
What does CH05 mean on an LG air conditioner?
CH05 means communication has been lost between the indoor and outdoor units. A tripped outdoor breaker is one possible cause, but wiring or control-board faults may also require investigation.
How do I clear the LG CH05 code?
Turn off power to both the indoor and outdoor units, wait about five minutes, and restore power to both sections together. Arrange service if the code returns.
Can a dirty filter cause CH05?
A dirty filter is not the normal direct cause. CH05 is defined as an indoor-to-outdoor communication fault, while a blocked filter is mainly an airflow and performance issue.
Why does CH05 return after a reset?
The reset may temporarily restore communication, but an intermittent power supply, loose connection, damaged cable or control-board problem can cause the fault to return.
Are CH05 and CH53 the same?
Both may relate to communication on certain LG systems, but they can identify the fault from different parts of the system or follow different diagnostic logic. Do not assume they are identical without checking the model-specific service information.
Can I reset a tripped air-conditioner breaker?
You may reset it once when there are no signs of damage, heat, smoke or water exposure. Stop and call a professional if it trips again.
Does CH05 mean the outdoor PCB must be replaced?
No. The code does not prove that either PCB has failed. Power supply and interconnecting wiring should be checked before a technician decides that a circuit board requires replacement.
Why did CH05 appear immediately after installation?
Incorrectly matched terminals, a loose connection or an unpowered outdoor unit are possible installation-related causes. LG’s installation guide specifically links mismatched wiring with CH05 and CH53.
Emily Carter is an Australian home-appliance safety editor with 9 years of experience researching washers, air conditioners, refrigerators, and coffee machines. She checks troubleshooting steps for accuracy, regional model differences, and homeowner safety before publication.