Check these first, whatever the brand
- Check the breakers
Look for a tripped circuit breaker or an isolator switched off next to the outdoor unit. LG puts a tripped breaker for the outdoor unit first on its list for CH05.
- Reset once at the air conditioner's own breaker
Switch it off, wait, then switch it back on. Daikin says to wait 20 minutes; LG says 3 to 5 minutes. Use the air conditioner's breaker, not the main switch for the whole house.
- Give it a few minutes
After power comes back, the units need a little time to find each other. Mitsubishi Electric allows up to 6 minutes before the indoor unit flags E6.
- Write the code down
If it comes back, note the exact code and the model number. The engineer will ask for both.
- New installation?
LG says a communication code that appears soon after installation often means a loose connection. Call the company that fitted it.
When it's time for an engineer
If the power is on and the code returns after a reset, an engineer will check the cable and terminals between the units, then the control boards on each side. The cable carries mains voltage, so leave it alone.
Questions people ask
What does a communication error mean on an air conditioner?
The indoor and outdoor units can't exchange signals, so the system stops. Daikin shows it as U4, Mitsubishi Electric as E6, LG as CH05 and Samsung as E101.
Can a power cut cause an air conditioner communication error?
Yes. Samsung says a cut in power to either unit can trigger E101, and a reset at the breaker often clears it. If the code keeps coming back, have it checked.