LG Heat Pump Error Code E431

E431 indicates that the outdoor unit compression ratio has exceeded 8.5 for more than 5 continuous minutes. The compression ratio is the relationship between high-side discharge pressure and low-side suction pressure. When this ratio stays too high, the system triggers the error to protect the compressor from damage. Common causes include low refrigerant, closed service valves, a faulty EEV, or a malfunctioning PWM valve.

No, continuing to operate the system with an active E431 error is not advisable. A compression ratio above 8.5 places extreme mechanical stress on the compressor, and prolonged operation under these conditions can result in compressor burnout, which is a significantly more costly repair. The system should remain off until the underlying cause is diagnosed and corrected.

A manual reset may temporarily clear the E431 code and allow the unit to restart, but if the underlying problem is not corrected, the error will return once the compression ratio exceeds 8.5 again for more than 5 minutes. Resetting without diagnosing the cause risks further damage to the compressor. The error should be treated as a warning to investigate and repair the root cause rather than a fault to simply clear.

Some preliminary checks, such as confirming that the service valves on the outdoor unit are fully open, can be done without special tools. However, diagnosing and correcting refrigerant charge issues requires EPA Section 608 certification and proper manifold gauge equipment. EEV and PWM valve testing also requires technical knowledge and tools, so most of the diagnostic work is best handled by a qualified HVAC technician.

Repair costs vary widely depending on the root cause. A refrigerant recharge typically runs between $150 and $400 depending on refrigerant type and the amount needed. An EEV replacement can cost between $200 and $600 including labor, while a PWM valve repair or replacement may range from $150 to $500. If the compressor has already been damaged due to running under high compression ratio conditions, costs can reach $1,000 to $2,500 or more.