CH05 - The indoor and outdoor units are not communicating, often because the outdoor unit has lost power.
LG's system-air-conditioner support page says CH05 occurs when there is a communication problem between the indoor and outdoor units. For ceiling-mounted system installations, LG specifically calls out a tripped outdoor-unit circuit breaker as a common cause, especially where indoor and outdoor units use separate breakers.
Based on LG USA support pages covering ceiling-mounted and system air conditioners; breaker layout, display style, and wiring arrangements can vary by installation.
Severity
High
Display
On applicable ceiling-mounted or system installations, CH05 appears on the controller or unit display when communication fails.
Support first?
Often not
Models in range
Ceiling-mounted system air conditioners, Multi-room system air conditioners
What to do first
Start with these checks
- 1Check whether the outdoor-unit breaker is tripped.
- 2If the outdoor breaker tripped, switch the indoor breaker off too, wait about 3 minutes, and restore both breakers at the same time as LG instructs.
- 3Stop if there is no dedicated outdoor breaker or if the breaker will not stay on.
Likely causes
What usually sits behind this code
Outdoor-unit circuit breaker is tripped.
Indoor and outdoor units are on separate breakers and were not restarted together.
Indoor-to-outdoor communication fault.
Contact support
Contact customer support if any of these apply
- !The breaker keeps tripping.
- !There is no dedicated outdoor breaker and the cause is unclear.
- !CH05 remains after the simultaneous breaker reset.
- - LG's newer system-specific article uses a 3-minute breaker-off interval.
- - The support page notes breaker layouts can differ between installations.
More ranges
More LG air-conditioner ranges
Source notes
Source and scope
Source: LG USA Support
LG says system-air-conditioner CH05 is a communication fault often caused by a tripped outdoor-unit breaker and recommends resetting indoor and outdoor breakers together after 3 minutes.
Last reviewed: 2026-04-19
Only operate clearly labeled breakers that are safe and accessible. If breaker behavior is abnormal, stop and use professional service.