LG Heat Pump Error Code E304

E304 indicates an OPEN or SHORT fault in the COND-OUT SUB 1 temperature sensor circuit. This sensor monitors temperatures at the condenser outlet sub-cooling section, and the control board has detected a resistance reading outside the acceptable range. The system flags this fault to prevent operation under inaccurate thermal conditions, which could damage the compressor or reduce efficiency.

It is not recommended to continue running the system while E304 is active. The control board relies on the COND-OUT SUB 1 sensor to regulate refrigerant flow and compressor operation, and running without valid sensor data can lead to compressor damage or system inefficiency. Address the fault before resuming normal operation.

Repair costs depend on the cause. Reseating a connector or repairing a damaged wire may cost relatively little in labor, typically in the range of $75 to $150 for a service call. A replacement temperature sensor generally adds $20 to $80 in parts. If the control board is at fault, parts and labor combined can range from $300 to $700 or more depending on the specific model and local labor rates.

Some causes of E304 are accessible to a knowledgeable DIYer, particularly checking and reseating the sensor connector or inspecting the wiring harness for visible damage. Measuring sensor resistance with a multimeter is also a straightforward diagnostic step. However, if the sensor or control board needs replacement, or if refrigerant system access is involved, a licensed HVAC technician should perform the work.

A power reset may temporarily clear the error code, but if the underlying sensor, wiring, or connector fault is still present, E304 will return once the system restarts and the control board re-checks the sensor circuit. A reset is useful for confirming whether the fault is intermittent, but it is not a substitute for diagnosing and correcting the root cause.