LG Heat Pump Error Code P742

P742 indicates that the outdoor unit discharge temperature sensor 2 has detected a temperature high enough to trigger protection control, causing the unit to shut down. This protects the compressor from heat-related damage. The code points to a problem in the refrigerant circuit, outdoor airflow, or the sensor itself. A technician should diagnose the root cause before restarting the system.

No. P742 is a protection code that the system activates specifically to prevent compressor damage from excessive discharge temperatures. Attempting to bypass or repeatedly reset the unit without addressing the underlying cause risks permanent compressor failure, which is one of the most expensive repairs on a heat pump system. Leave the unit off until a technician has diagnosed and corrected the problem.

Repair costs vary significantly depending on the root cause. A refrigerant recharge, including leak detection and repair, typically runs in the range of $200 to $600 or more depending on refrigerant type and the extent of any leaks. Replacing a discharge temperature sensor is generally a lower-cost repair, often in the $100 to $250 range including labor. Outdoor fan motor replacement usually falls in the $150 to $400 range, while compressor replacement, if required, can cost $800 to $2,000 or more.

Some basic checks, such as clearing debris from around the outdoor unit and making sure the coil is clean, can be done without professional help. However, checking refrigerant charge requires certified technician equipment and EPA 608 certification to handle refrigerants legally. Sensor testing and fan motor diagnosis also benefit from professional tools, so most repairs associated with P742 should be performed by a qualified HVAC technician.

A power cycle reset may temporarily clear the code and allow the unit to restart, but if the underlying cause, such as low refrigerant, a blocked coil, or a failing fan, has not been corrected, the code will return. Repeated triggering of the protection control without resolving the root cause can lead to accelerated wear or failure of the compressor. A reset should only be used after the underlying issue has been identified and fixed.