Indoor and Outdoor Communication
LG CH05 Error Code
The LG CH05 error code is a communication fault. Your indoor unit has stopped receiving proper signals from the outdoor unit, so it shuts the system down rather than run without instructions. Causes range from a tripped breaker to damaged wiring or a failed board, and this page helps you work out where to start.
What It Means
Why Does My LG Say CH05?
An LG split system is really two machines working as a team. The indoor unit handles airflow and reads the room. The outdoor unit houses the compressor and the inverter that drives it. They swap information constantly through a communication wire that runs alongside the refrigerant pipes.
That conversation covers everything. The indoor unit asks for more or less cooling, and the outdoor unit reports back on its temperatures, its speed and any problems. When the indoor board stops hearing valid replies for long enough, it raises CH05 and stops.
LG describes the fault as a communication failure from the indoor unit to the outdoor unit. A closely related code, CH53, describes the same breakdown seen from the outdoor side. Either way, the units have lost touch with each other.
The important thing to understand is that CH05 tells you about the link, not the exact broken part. The cause can sit anywhere along that chain, which is why careful diagnosis matters more here than with most codes.
The Chain
Which Parts Are Involved in a CH05 Fault?
Think of the communication path as a chain with several links. A break in any one of them produces the same code. A technician tests each link in turn.
Power to the Outdoor Unit
On many installs the outdoor unit has its own breaker or isolator. If that power is off, the outdoor board cannot answer, and the indoor unit shows CH05.
The Interconnecting Cable
The cable between the units carries power and data. It runs through walls, roof spaces and along external brackets, where it can be damaged.
Terminal Connections
Each end of the cable lands on a terminal block. Loose screws, corrosion or wires in the wrong terminal all break the signal.
The Control Boards
Both the indoor and outdoor boards have communication circuits. Lightning, surges and age can damage them, leaving the units unable to talk.
On some LG models, the outdoor inverter must power up fully before it can communicate. A fault in the outdoor power supply section can therefore look like a communication problem, even though the wiring is perfect.
Where You Will See It
How Does CH05 Appear on the Display?
On LG wall splits with a numeric display, CH05 shows as CH alternating with 05 or 5. The indoor fan may run briefly at start up before the code appears, because the unit only realises the outdoor side is silent after a short wait.
Units with indicator lights only will blink a repeating pattern. Film the lights through at least two full cycles. Ducted systems show the code on the wall controller, and multi split systems may show the code on every connected indoor unit at once if the outdoor unit has gone quiet.
Timing is a useful clue. A code that appears within a minute or two of switching on often points to power or wiring. A code that appears after the system has run for a while can point to a component that fails as it warms up.
Ranked Causes
What Are the Most Likely Causes of LG CH05?
Communication faults have a wide spread of causes. The list below starts with the simplest, likeliest causes and moves towards the ones that need a technician with test equipment.
Check These First
- The outdoor unit breaker or isolator switched off or tripped
- A power interruption that left the boards out of step
- A storm surge that briefly scrambled the outdoor board
- Recent building work that disturbed the interconnecting cable
Technician Territory
- Loose or corroded terminals at either unit
- A cable chewed by rodents or crushed in a roof space
- Water entry into the outdoor electrical compartment
- A failed communication circuit or power supply on a board
New installations and relocated units deserve special mention. If CH05 appears on the very first start, the cause is often wiring. A conductor in the wrong terminal, or a cable that does not meet the requirements for the run length, can stop communication from day one.
Your Checks
What Should I Check When CH05 Appears?
CH05 is one of the few LG codes where your own checks can genuinely fix the problem, because a switched off outdoor supply is a frequent cause. Stay with the switches and the outside of the units.
- Write down or photograph the code.
- Look at your switchboard for a tripped breaker or safety switch labelled for the air conditioner.
- Check the outdoor isolator switch, the weatherproof switch on the wall near the outdoor unit. Make sure it is in the on position. Do not open it up.
- If anything had tripped, reset it once. If it trips again straight away, leave it off.
- With everything on, switch the unit off at the breaker for five minutes, then restore power and try again.
- Look along the visible cable route outside for obvious damage, such as a cut cable, a broken conduit or a cable pulled from its clips. Do not touch damaged cable.
If the outdoor unit makes no sound at all when the indoor unit asks for cooling, mention that when you book. It suggests the outdoor side has no power or has not woken up.
Also note whether other appliances lost power at the same time, or whether a neighbour mentioned an outage. That information helps separate a household wiring issue from a grid event. If the safety switch keeps tripping when the air conditioner starts, a licensed electrician or air conditioning technician needs to find the leak to earth before the system is used again. Never hold a breaker or safety switch in the on position, and never swap it for a larger one.
Safety First
Is It Safe to Keep Using an LG Unit With CH05?
The unit will not cool or heat while CH05 is active, because the compressor will not run without instructions. In that sense it protects itself.
The safety concern is electrical. If your check found a breaker that trips again on reset, or a damaged cable, leave the system off at the breaker. A cable or board fault can heat up or arc, and repeated resets put stress on parts that are already struggling.
If the code simply returns after a reset with no tripping, the risk is lower, but there is still no benefit in trying again and again. Switch the unit off and book a technician to trace the fault.
Diagnosis
How Does a Technician Trace an LG CH05 Fault?
A good communication diagnosis is systematic. The technician works from the power supply outwards, checking each link of the chain rather than guessing at boards.
Confirm Supply Voltage
They measure the supply at the outdoor unit and the indoor unit to make sure both are receiving correct power.Inspect Terminals
With power isolated, terminal blocks at both ends are inspected for tightness, corrosion, burnt marks and correct wiring order.Test the Cable
Each conductor in the interconnecting cable is checked for continuity and for faults between conductors or to earth.Watch the Signal
With power restored, they check the communication voltage, which should fluctuate as the boards exchange data. A flat reading shows where the signal stops.Read Board Status Lights
The outdoor board status lights reveal whether that board has powered up and is attempting to communicate.Repair the Faulty Link
The fix might be tightening a terminal, replacing a section of cable, or replacing a board. The system is then run to confirm stable communication.
Open more detail
Replacing a board without proving the wiring first is a common and costly mistake. A damaged cable can make a brand new board look faulty, and in some cases a short in the cable can damage the replacement board too. That is why careful technicians test the cable and terminals before ordering parts.
On multi split systems, the technician also checks whether the fault affects every indoor unit or just one. If only one unit shows CH05, the problem is usually in that unit’s cable or board. If all show it, the outdoor unit is the focus.
New or Established
Does CH05 Mean Something Different on a New Install?
The code means the same thing, but the likely cause changes depending on the age of the installation. Knowing which situation you are in helps decide who to call first.
Brand New or Just Relocated
If CH05 appears on the first start, or within days of an install, wiring is the prime suspect. Conductors may be swapped between terminals, or the cable may not suit the run. Contact the original installer, since this is part of their work.
Running Well for Years
An established system that suddenly shows CH05 points more towards power events, corrosion, cable damage or a failing board. This is where a fresh diagnosis by a licensed technician makes sense.
There is a middle ground too. A system that showed CH05 occasionally from new and is now showing it more often may have had a marginal connection from day one. Heat and vibration have slowly made it worse. The technician will look closely at the terminals in that case.
Intermittent Faults
Why Does CH05 Come and Go?
Intermittent communication faults frustrate owners and technicians alike. The unit works perfectly on the day of the visit, then fails again a week later. There are usually good reasons for that pattern.
A terminal that is slightly loose may connect well when cool and lose contact as it warms up in the afternoon sun. A cable with a small nick may only short when it is wet after rain. A board component that is starting to fail may work until it reaches a certain temperature. Each of these produces a code that seems random but actually follows conditions.
That is why a simple log is so valuable. Note the date, time, weather and how long the unit had been running when the code appeared. A pattern such as hot afternoons only, or wet days only, can lead the technician straight to the cause. Photos of the display each time help as well. Even a rough record kept on your phone over a couple of weeks can save a lot of guesswork.
Weather and Power
Do Storms and Power Outages Cause CH05?
Very often, yes. Summer storms are a regular trigger for communication faults across Australia. A nearby lightning strike or a surge on the grid can upset or damage the delicate circuits that handle communication. Sometimes a simple reset fixes it. Sometimes the surge has damaged a component and a repair is needed.
Power interruptions can also leave the indoor and outdoor boards restarting at different moments. They may fail to reconnect until both are power cycled together, which is why a full reset at the breaker is worth trying.
Other climate factors work more slowly. Coastal salt air corrodes outdoor terminal blocks over years, until one day the connection fails. Heavy rain driven sideways by wind can find its way into poorly sealed electrical compartments. In hot, dry areas, cable insulation exposed to direct sun can become brittle and crack. Rodents seeking shelter in roof spaces during cooler months sometimes chew through cables.
Protecting the Link
How Can I Reduce the Risk of CH05?
You cannot control the weather, but a few steps lower the chances of a communication fault and make repairs simpler if one occurs.
Surge Protection
Ask a licensed electrician whether surge protection at your switchboard suits your home. It can reduce the impact of grid spikes on sensitive electronics, including air conditioners.
Protect Exposed Cable
Cable runs along external walls should be in conduit or ducting. If you notice damaged covers, have them repaired before the cable inside suffers.
Keep Outdoor Units Tidy
A clear area around the outdoor unit makes it easier to spot damage and reduces nesting spots for pests.
Related Faults
Which LG Codes Often Appear Alongside CH05?
Communication faults sometimes travel with power related codes, because they share some causes. These pages explain the neighbours.
LG CH21
A current spike in the outdoor inverter, sometimes seen after storms.
LG CH26
Compressor start failure, another outdoor unit fault.
LG CH67
Outdoor fan lock, which can follow damage to the outdoor unit.
Browse every code on our LG error code hub, or explore the wider error code library.
Getting a Technician Out
Where Do You Arrange CH05 Repairs?
We book licensed technicians for LG communication faults across the five largest capitals. Storm season can be busy in all of them, so it helps to call early with your code and model ready.
For brand specific information, see our LG air conditioning page or the city pages for LG in Sydney, LG in Brisbane, LG in Perth and LG in Adelaide. Rapid Air Cooling is a booking service, not affiliated with LG, and the technicians we send hold the licences their work requires.
Questions
Frequently Asked Questions
My LG showed CH05 after a blackout. What should I do?
Switch the unit off at the breaker for five minutes, then restore power. Boards sometimes fail to reconnect after an outage. If the code returns, book a technician.
Is CH05 the same as CH53?
They describe the same lost link from different sides. CH05 is reported from the indoor side and CH53 from the outdoor side. The diagnosis is very similar.
Does CH05 always mean a board has failed?
No. Power supply problems and wiring faults are common causes. A technician should test the cable and terminals before replacing any board.
The outdoor unit is completely silent. Is that related?
Very likely. A silent outdoor unit often means it has no power or has not powered up. Check the outdoor isolator and breaker, then book a technician if those are fine.
Why did CH05 appear after renovations?
Building work can crush, cut or disturb the cable between the units, especially in roof spaces and walls. Let the technician know about any recent work.
Can a new install show CH05?
Yes. On a new or relocated system, CH05 on first start often points to wiring. Contact the installer first if the work was recent.
Where can I learn about other common faults?
Our troubleshooting guide covers the basics, and our page on air conditioning service Australia explains how we arrange visits.
LG Units Not Talking?
Tell us you have a CH05 code and what you have already checked. We will arrange a licensed technician to trace the fault through power, wiring and boards.
Reviewed by AC repair and service specialist on 22 October 2026. How we write our articles