LG Heat Pump Error Code P731

P731 on an LG heat pump means the outdoor unit sump temperature exceeded 95 degrees Celsius for 5 continuous minutes, triggering the SUMP DOWN 1 protection control. The system shuts down automatically to protect the compressor from heat-related damage. The fault points to issues with the digital compressor capacity control, the PWM valve, or the sump temperature sensor itself.

No, continuing to operate the system with an active P731 fault is not recommended. The error indicates a critical overtemperature condition that has already triggered a protective shutdown. Attempting to bypass or ignore this fault risks severe compressor damage, which is one of the most costly repairs on a heat pump system.

Repair costs vary widely depending on the root cause. A temperature sensor replacement is relatively inexpensive, typically in the range of $100 to $250 including labor. A PWM valve replacement will generally cost more, often in the $200 to $500 range. If the compressor itself has been damaged by repeated overtemperature events, replacement costs can range from $800 to well over $2,000 depending on the unit size and labor rates in your area.

Some basic checks, like verifying that the outdoor unit has proper airflow and is not obstructed, can be done without special tools. However, diagnosing and repairing the PWM valve, digital compressor loading behavior, or temperature sensor requires refrigeration and electrical diagnostic knowledge. A qualified HVAC technician should perform the detailed inspection and any component replacement.

A power reset may temporarily clear the fault and allow the unit to restart, but if the underlying cause is not corrected, the sump temperature will rise again and the P731 code will return. Resetting without diagnosing the root cause can lead to repeated thermal stress on the compressor. The fault should be properly diagnosed before relying on a reset as a solution.