LG Heat Pump Error Code P804

P804 indicates that the MCU has detected a solenoid valve failure within the heat pump system. The solenoid valve controls refrigerant flow direction, and the MCU monitors its electrical circuit for proper operation. LG rates this as a low-level risk fault, meaning the indoor unit continues to function normally while the code is active. A technician should still diagnose and resolve the underlying cause to prevent escalation.

LG classifies P804 as a low-level risk fault, and the indoor unit is designed to continue operating normally when this code is present. In the short term, continued use is generally not a safety hazard. However, leaving a solenoid valve fault unresolved can lead to reduced system efficiency or additional component stress over time, so scheduling a service call promptly is advisable.

Resetting the unit by cycling power may temporarily clear the P804 code from the display, but if the underlying fault in the solenoid valve circuit remains, the code will return once the MCU detects the problem again. A reset is useful for confirming whether the fault is intermittent, but it does not address the root cause. A proper diagnostic inspection is needed to resolve the fault permanently.

Some basic checks, such as inspecting wiring connectors for looseness or corrosion and reseating them, can be performed by a knowledgeable DIYer. However, testing the solenoid coil resistance, diagnosing the MCU output circuit, and handling refrigerant-related components require proper tools and in some cases EPA certification. Most homeowners should call a qualified HVAC technician for this repair.

Repair costs vary depending on the root cause. If the fix is simply reseating a loose connector, the cost may be limited to a service call fee, typically in the range of $75 to $150. Replacing a faulty solenoid valve coil or valve assembly can range from $150 to $400 or more including parts and labor. If the MCU control board requires replacement, costs can rise to $300 to $700 or higher depending on the specific unit.