Quick answer
Error CH05 on an LG mini-split is a communication error between the indoor and outdoor units. The two units have stopped exchanging signals, so the system will not run. Switch the breaker off, wait at least 3 minutes, restore power, and confirm the outdoor disconnect is on. If CH05 returns, the transmission wiring and circuit boards need checking with a meter.
Error CH05 on an LG mini-split means the indoor and outdoor units have stopped communicating. LG's troubleshooting guide for its wall-mount inverter systems lists it as a communication error between the indoor unit and the outdoor unit. Each unit has its own circuit board, the boards trade signals over the cable that links them, and CH05 appears when that exchange fails. LG's code tables change between product generations, so check the label and manual for your model before acting on any general guide.
Why the system stops completely on CH05
The system will not run with CH05 showing. A mini-split depends on the two boards agreeing on what the compressor and fans should be doing, so when the link drops, both halves stop. There is nothing to gain from leaving it switched on and waiting; it will not heat or cool until communication is back.
The safe reset: breaker off, 3 minutes, power back on
LG warns that nothing should be checked until 3 minutes after the power is switched off. Treat that as the minimum wait for a reset as well.
- Find the breaker for the mini-split in the electrical panel and switch it fully off.
- Wait at least 3 minutes. Use a timer; a short pause is not enough.
- While you wait, go to the outdoor unit and look at the disconnect box on the wall beside it. Confirm it is in the on position and the cover is seated.
- Switch the breaker back on and start the system from the remote.
- If CH05 returns, leave the system off and do not open either unit.
If the breaker will not stay on, that is a different and more urgent problem than a code: leave it off and call. Why a mini-split will not turn on covers the power-side checks in more detail.
What causes CH05, most likely first
- No power to one of the units. A tripped breaker, or an outdoor disconnect left off after yard work, painting or a service visit, means one board is dark and the other gets no reply.
- A disconnected or wrongly terminated communication wire. A loose or misplaced termination at either end of the cable between the units breaks the signal.
- External electrical noise interfering with the signal on the cable.
- Burned parts in the communication circuit on one of the circuit boards (PCBs), which a technician confirms only after the first three are ruled out.
New install or older system? The history narrows it down
On a system that has never worked properly since installation, the wiring terminations are the first suspect, and that is a call to the installer. On a system that ran for years and threw CH05 after a storm, an outage or a breaker trip, the power supply and the boards move to the top of the list. Tell the technician which describes yours.
Mini-splits in our area tend to serve the spaces a ducted system never reached: a garage workshop, a third-floor room in a pre-war brick house in Hamilton, an addition on a 1960s bungalow. Those installs can have long cable runs through unheated space, and every extra metre is more cable to inspect.
What a technician tests on a CH05 call, and what it costs
The transmission wiring and the boards need checking with a meter. That means confirming supply voltage at both units, inspecting each termination, testing the cable end to end, and then checking whether each board is sending and receiving. This is live electrical work inside both units, so it is not a homeowner job, and electrical repairs in Ontario fall under ESA rules.
- Diagnostic visit: $90–$150, taken off the repair bill if you proceed
- Re-terminating or replacing the interconnecting cable: quoted in writing, because the price depends on the length and route of the run
- Replacement circuit board: quoted in writing by model number, since board prices differ widely between units
ZK Mechanical repairs ductless systems across Burlington, Oakville, Milton, Hamilton and Mississauga. For a CH05 that survives a proper reset, book heat pump repair or mini-split repair, or send us the model number and the code. The LG mini-split error code guide lists the other CH codes, and why a mini-split light is blinking helps if your unit shows flashes instead of a number.