LG Mini-Split Error Codes: What Each CH Code Means and What to Do

LG mini-splits display error codes in CH format — CH01, CH09, CH21, and so on — on the indoor unit’s LED display when a fault is detected. The CH codes are grouped by system:

• CH01–CH05: temperature sensor faults (room temp, coil temp, outdoor sensors)
• CH07: outdoor fan motor fault
• CH09 / CH10: communication errors between indoor and outdoor units
• CH21–CH27: protection codes (high pressure, low pressure, compressor, power)
• CH38: inverter fault
• CH44: wiring / connection error

CH09 (communication error) and sensor faults (CH01–CH05) have DIY-accessible first steps. The protection and compressor codes almost always need a technician with gauges and EPA 608 certification.

The installation manual for your model is the definitive code reference. LG has updated CH code assignments between product generations — confirm codes against the manual’s fault code table.

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How to read and clear LG CH codes

Reading a code: When a fault occurs, the CH code appears on the indoor unit display. On units with a remote controller display, the code may also appear on the remote.

Entering self-diagnostic mode: On many LG mini-splits: press the + and — buttons on the indoor unit simultaneously for 3 seconds, or check the FUNCTION/SET button sequence in your manual. Some models require a specific sequence on the remote.

Clearing/resetting: Turn the unit off from the remote. Wait 3–5 minutes. Turn it back on. If the fault condition is resolved, the code clears and the unit resumes operation. If the fault is still present, the code returns immediately or within the first cycle.

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LG mini-split CH error codes: full list

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Code-by-code: what to check first

CH09 — Communication error (the most common DIY-addressable code)

The indoor and outdoor units have lost the serial communication signal.

What to check:

1. Check the communication wiring terminals. In the indoor unit (remove front panel to access terminal block) and at the outdoor unit terminal block. LG mini-splits use a 3-wire or 4-wire communication setup, often with terminals labeled L1, L2, L3 or similar.

1. Confirm the wires are tight. With power off, loosen each terminal screw and re-seat the wire, then retighten. Vibration can loosen connections over years of operation.

1. Inspect the communication cable run — from the indoor unit out through the wall to the outdoor unit. Look for physical damage: UV cracking on the outdoor section, compression at wall penetrations, any point where the cable may have been pinched.

1. Confirm power to both units. CH09 appears if the outdoor unit has no power (tripped breaker, blown disconnect fuse, loose disconnect) even if the wiring is intact. Check the outdoor disconnect and circuit breaker.

1. Rule out mismatched units. If the system was recently serviced and a component replaced, confirm the indoor and outdoor units are a compatible matched pair.

CH09 that persists after checking connections and power typically requires a technician to test the communication circuit and identify whether the indoor PCB, outdoor PCB, or cable is at fault.

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CH01 — Room temperature sensor error

The thermistor measuring indoor air temperature has failed or its connector has come loose.

What to check:

• Open the front panel. The room temp sensor is a small thermistor, often located in the return air path near the filter or in a pocket on the indoor unit chassis.
• Check the connector where the sensor wire plugs into the control board. A loose connection after cleaning or service is common.
• If secure and code persists: sensor has failed. A tech can test resistance at known temperatures and replace the thermistor ($10–20 part, labor needed for LG-specific connector types).

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CH02 — Indoor coil (heat exchanger) temperature sensor error

Same diagnostic as CH01, but the sensor is clipped to the evaporator coil fins. Check the connector at the board; if connected and code persists, sensor replacement needed.

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CH21 — Protection device activated (outdoor unit)

The outdoor unit’s high-pressure safety switch opened. This is a protection shutdown, not a wiring fault.

What to check yourself:

• Is airflow to the outdoor unit blocked? Clear debris from around the unit (leaves, grass, snow). Ensure 12+ inches clearance on all sides.
• Is the outdoor condenser coil dirty? Rinse from the inside outward with a garden hose (power off) to remove debris from fins.
• Is the outdoor fan running? Confirm the fan blade is turning during operation.

If airflow is clear and CH21 returns: refrigerant system issue (overcharge, restriction). Call a technician.

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CH23 — High pressure protection

Same as CH21, but triggered by the pressure transducer rather than the safety switch. The system detected compressor discharge pressure above the upper limit.

Check airflow as above. If airflow is clear, refrigerant system diagnostic required.

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CH24 — Low pressure protection

Suction pressure dropped below the lower limit — most commonly from refrigerant undercharge due to a slow leak.

This requires a technician. Refrigerant recovery, leak detection, repair, and recharge all require EPA 608 certification. Do not attempt to add refrigerant without recovering first and weighing in the correct charge.

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CH22 — Compressor overload protection

The compressor drew excessive current or reached an overtemperature condition. Possible causes: failing compressor, high discharge pressure (same as CH23), low voltage at the outdoor unit.

Call a technician. Compressor current testing requires a clamp meter and manifold gauges.

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CH44 — Miswiring / connection error

The system detected a connection that doesn’t match the expected electrical configuration. This code commonly appears after installation or service where terminals were connected incorrectly.

Call the installing contractor — this is a wiring or configuration error, usually at the terminal block. Do not attempt to rearrange electrical connections without confirmed knowledge of LG’s terminal layout.

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When to call an HVAC technician

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FAQ

What does CH00 mean on an LG mini-split? CH00 typically indicates a normal operating state on LG units — not a fault. It may display briefly when the diagnostic mode is entered but no fault is stored. If CH00 appears and the unit is running normally, no action is needed.

My LG mini-split shows a CH code but then clears itself. Should I be concerned? An intermittent code often indicates a marginal condition — a borderline sensor, a connection that’s sometimes loose, or an operating condition that briefly pushes the system into protection mode. If it clears and doesn’t return, monitor it. If it appears more than once within a season, investigate before it becomes a no-cooling situation on the hottest day.

How do I find the installation manual for my LG mini-split? Your model number is on the nameplate on the indoor unit chassis (usually visible with the front panel open). Search for “[model number] installation manual PDF” — LG publishes manuals for all current models on lghvac.com. Manuals include the fault code table specific to your board.

Can I add refrigerant to my LG mini-split myself? No. LG mini-splits use R-410A or R-32, both of which require EPA 608 certification. Adding refrigerant requires: a recovery unit to capture existing refrigerant first (if the circuit needs to be opened), a vacuum pump to evacuate after any service, and weighing in the correct charge by mass. Overcharge causes CH23/high-pressure faults; undercharge causes CH24/low-pressure faults. Both cause compressor damage over time.

The CH code shows on my remote but not the indoor unit. Is that normal? Yes — on many LG models, the remote controller mirrors the fault display from the indoor unit, and some faults may appear there first or more visibly. Both displays should show the same code.

Related reading

For the equivalent blink-code system on a different brand, see Fujitsu mini-split blink codes, which uses a two-light pattern instead of LG’s CH-prefixed numeric codes.