Indoor unit displays CH01 and will not operate or stops shortly after starting.

Safety first: Turn off the indoor unit and switch off the breaker supplying the air conditioner before removing any covers.

Steps to check and attempt repair:

• Power reset: Turn the breaker OFF for 5 minutes, then ON again. Try operating the unit to see if CH01 clears. If it returns, continue.
• Access the indoor PCB: Remove the front grille and filter, then remove the screws securing the front cover to expose the control board and sensor wiring.
• Locate the room thermistor: It is usually clipped near the indoor coil inlet or in the return air path, with two small wires going to the PCB.
• Check connections: Ensure the thermistor plug is fully seated on the PCB and that there are no broken or pinched wires. Reseat the connector several times to clean contacts.
• Inspect the sensor: Look for physical damage, corrosion, or broken insulation. If the sensor is loose from its clip, reattach it firmly in the airflow path.
• Test continuity (advanced): With power still OFF, use a multimeter to measure resistance across the thermistor leads. An open circuit or 0 Ω indicates a failed sensor.
• Replace if faulty: If the thermistor is open/shorted or visibly damaged, replace it with an LG-compatible indoor room thermistor for your exact model. Route the new sensor wiring along the original path and secure with clips or ties.
• Reassemble and test: Refit the covers and filters, restore power, and run the unit in COOL mode to confirm the error is cleared.

When to call a technician: If the thermistor and wiring test good, the indoor PCB may be defective and should be diagnosed and replaced by a qualified technician.