LG Heat Pump Error Code E504

E504 on an LG heat pump indicates that the unit experienced an instant, uncontrolled power loss during its previous operating cycle rather than a normal shutdown. The code is stored in the control board's memory and displayed until the compressor runs successfully again, at which point it clears automatically. It is most commonly caused by a power outage, a tripped breaker, or a momentary supply voltage interruption.

A single occurrence of E504 following an obvious event like a power outage is generally not a safety concern, and the unit should resume normal operation on its own. However, if the code appears repeatedly without an obvious cause, you should stop using the unit and have a qualified technician inspect the electrical supply and internal components to rule out an overcurrent or wiring fault that could pose a risk.

If the cause is simply a power outage or a tripped breaker, there is no repair cost beyond a service call fee if you choose to bring in a technician. If a component such as a contactor or control board needs replacement, repair costs can range from around $150 to $600 or more depending on the part, labor rates in your area, and whether the unit is still under warranty. A compressor replacement, if required, would be significantly more expensive.

The E504 code is designed to disappear on its own once the compressor runs successfully, so a full power reset is not always necessary. However, cycling power at the breaker or disconnect can help the unit attempt a fresh startup. If the code clears after a normal run cycle, no further action may be needed unless it reappears frequently.

Start by checking your electrical panel for a tripped breaker and resetting it if needed. Verify that the unit's disconnect box is fully engaged and that all visible wiring connections are secure. If the code clears after the unit completes a run cycle, monitor for recurrence. Persistent or repeated E504 faults require inspection of the supply voltage, wiring harness, compressor, and contactor by a qualified technician.