LG Heat Pump Error Code P511

P511 means the heat pump has shut down the compressor due to low pressure sensor protection control 2. The system detected that suction-side refrigerant pressure fell below a safe threshold, so the control board forced a shutdown to prevent compressor damage. Common causes include refrigerant loss, blocked airflow, a faulty expansion valve, or a defective pressure sensor. A qualified technician should diagnose the root cause before the unit is restarted.

No. The P511 code indicates the system has already shut itself down to protect the compressor from damage. Attempting to repeatedly restart the unit and force it to run without addressing the underlying cause can result in compressor failure, which is one of the most expensive components in the system. Leave the unit off and schedule a service call.

A power cycle reset may temporarily clear the P511 fault and allow the unit to restart, but if the underlying cause such as a refrigerant leak or faulty component is still present, the error will return and the compressor will shut down again. Repeated resets without fixing the root cause risk permanent compressor damage. A proper repair addressing the source of the low pressure condition is required for the fault to stay cleared.

Some basic checks, like inspecting and replacing dirty air filters or clearing debris from the outdoor unit, can be done without professional help. However, diagnosing refrigerant leaks, recharging the system, or replacing components like the expansion valve or pressure sensor requires EPA Section 608 certification and specialized tools. Attempting refrigerant-side repairs without proper training and equipment is unsafe and may be illegal.

Repair costs vary widely depending on the root cause. Cleaning coils and replacing filters may cost between $75 and $200 for a service visit. Refrigerant leak repair and recharge can range from $300 to $800 or more depending on leak location and refrigerant type. Expansion valve replacement typically falls between $250 and $600 in parts and labor. Pressure sensor replacement is generally less expensive, often in the $150 to $400 range.