LG Heat Pump Error Code P771

P771 indicates that the outdoor unit has measured a compression ratio greater than 8.5 for more than 5 continuous minutes. The compression ratio is the relationship between the compressor discharge pressure and suction pressure. When this ratio is too high for too long, it signals an abnormal refrigerant flow condition that can stress or damage the compressor. Common causes include closed service valves, a faulty EEV, incorrect refrigerant charge, or a malfunctioning PWM valve.

Running the system while the P771 error is active is not recommended. A sustained high compression ratio places excessive mechanical stress on the compressor, which can lead to premature failure. Continued operation under these conditions risks turning a relatively low-cost repair into a full compressor replacement. It is best to shut the unit down and call a technician promptly.

Repair costs vary widely depending on the root cause. A simple service valve adjustment or minor refrigerant top-off may cost between $100 and $300 for a service call and labor. Replacing an EEV or PWM valve can range from $250 to $700 or more including parts and labor. If the compressor has already been damaged by the condition that caused P771, replacement costs can reach $1,000 to $2,500 or higher depending on the system size and refrigerant type.

Some preliminary checks, such as confirming the service valves are fully open, can be performed without special tools or certifications. However, diagnosing refrigerant charge, EEV function, and PWM valve operation requires manifold gauges and technical knowledge. Any work involving refrigerant handling must be performed by an EPA 608 certified technician. Attempting repairs beyond valve inspection without proper training risks injury and further system damage.

Resetting the unit may temporarily clear the fault display, but the error will return if the underlying cause has not been corrected. The control board triggers P771 only after the compression ratio has exceeded 8.5 for more than 5 minutes, so the condition causing the imbalance must be diagnosed and repaired for the code to stay clear. A reset alone is not a fix.