LG Heat Pump Error Code E204

E204 on an LG heat pump means the system has detected a communication error between the outdoor unit and the MCU (microcontroller unit). The indoor and outdoor units exchange data via a DC square wave signal at approximately plus or minus 0.7 volts, and this signal has been lost or corrupted. The system halts normal operation when this error is active to protect the equipment.

Pressing the K3 reset key can clear the E204 error if the communication disruption was temporary, such as from a minor power fluctuation or a briefly loose connector. If the underlying wiring or component fault is still present, the error will return after reset. A reset is always the recommended first step, but a recurring E204 requires hands-on diagnostic work.

Repair costs vary depending on the cause. If the fix is simply reseating a connector or replacing a communication wire, costs typically range from around $75 to $200 including labor. If a control board or MCU replacement is needed, costs can range from $300 to $700 or more depending on parts pricing and local labor rates.

A homeowner can safely start by checking that all wiring connections between the indoor and outdoor units are secure and by pressing the K3 reset key to clear the fault. However, advanced diagnosis requires an oscilloscope to measure the communication signal, and board replacement requires proper handling of electrical components. If the error returns after a reset, a qualified technician should perform further diagnosis.

No, you should not attempt to run the heat pump while E204 is active. The error indicates the indoor and outdoor units are not communicating properly, which means the system cannot coordinate safe operation between its components. Running the unit in this state could result in incorrect operation or equipment damage.