LG Oven Error Code C-21

C-21 means the oven control board has detected either an abnormally high internal temperature or a shorted oven temperature sensor during operation. The temperature sensor is an RTD probe that should measure approximately 1080 ohms at room temperature. When it shorts, the resistance drops dramatically and the board flags the condition as a C-21 fault. The oven should not be used until the underlying cause is identified and corrected.

No, you should not operate the oven while C-21 is active. The error indicates either a sensor fault that prevents accurate temperature regulation or an actual overheating condition, both of which pose a risk of scorched food or fire. Disconnect power and leave the oven off until the fault is diagnosed and repaired.

If the oven temperature sensor is the cause, the part itself typically costs in the range of $20 to $60, and the repair is relatively inexpensive if done without a service call. A professional diagnosis and sensor replacement can run $100 to $250 depending on labor rates in your area. If the control board is at fault, parts alone can range from $150 to $350 or more, making professional repair costs considerably higher.

A knowledgeable DIYer can diagnose C-21 by disconnecting power, unplugging the sensor harness, and measuring sensor resistance with a multimeter. If the reading is far below 1080 ohms, replacing the temperature sensor is a straightforward repair that typically involves removing one or two mounting screws inside the oven cavity. Harness damage or a faulty control board requires more involved repair work and may warrant a professional technician.

Disconnecting power for a few minutes may temporarily clear the code, but it will return as soon as the oven attempts to operate if the underlying fault has not been fixed. A shorted sensor or damaged harness will continue to trigger C-21 until the defective component is repaired or replaced. Reset should only be used as part of a diagnostic process, not as a long-term solution.