LG Air Conditioner Error Code 151

Error code 151 on an LG air conditioner signals a failure in operation mode conversion at the outdoor unit, caused by a functional error with the 4-way reversing valve. This valve controls the direction of refrigerant flow to switch between heating and cooling modes. When the control board commands a mode change and the system cannot confirm the valve has shifted, this code is displayed. The unit will be unable to switch operating modes until the issue is resolved.

Continuing to operate the unit with error code 151 active is not recommended. The system cannot properly switch between heating and cooling modes, which means it may be stuck in one mode or fail to condition your space effectively. Running the system in a faulted state can also place additional stress on other components. It is best to address the underlying issue before resuming normal operation.

A power reset may temporarily clear the error display, but the code will return if the underlying fault with the 4-way valve has not been corrected. The control board monitors valve operation during every mode change command, so the failure will be detected again the next time the system attempts to switch modes. A reset is useful for confirming whether the fault is intermittent, but it is not a substitute for proper diagnosis and repair.

A homeowner or DIYer can safely check whether the 4-way valve connector at the outdoor unit is properly seated and free from corrosion, which is the first recommended diagnostic step. However, testing the solenoid coil, inspecting internal wiring, or evaluating refrigerant pressures requires technical knowledge and proper tools. Replacing the reversing valve or control board should be performed by a qualified HVAC technician, as it involves working with a sealed refrigerant system.

Repair costs vary depending on the root cause. If only the connector needs to be reseated, there may be no parts cost beyond a service call fee, typically in the range of $75 to $150. A replacement solenoid coil or reversing valve can add $100 to $400 or more in parts depending on the model, with labor costs on top of that. Control board replacement tends to be the most expensive repair, often ranging from $200 to $600 or more for parts and labor combined.