GE Oven Error Code F21

F21 means the control board has detected that the resistance on the upper oven sensor circuit has exceeded the acceptable threshold. The upper oven sensor is a probe inside the oven cavity that the control board uses to monitor temperature. The fault can originate from the sensor itself, the wiring between the sensor and the board, a loose connector, or in some cases the control board.

No, using the oven while F21 is active is not recommended. The error indicates the control board cannot accurately read the upper oven temperature, which means it cannot regulate heat properly. Continuing to use the oven in this condition risks uncontrolled temperatures and potential fire hazard. Leave the oven off until the fault is diagnosed and repaired.

Yes. A loose or corroded connection at CN300 on the ERC or J300 on the machine control board adds resistance to the sensor circuit, which the control board reads as a fault even if the sensor itself is fine. Before replacing any parts, inspect and firmly reseat the connectors on both ends of the upper oven sensor wiring harness. This step is specifically included in GE's first diagnostic step for F21.

Start by disconnecting power and checking the resistance of the upper oven sensor circuit at CN300 pins 1 to 3 (W to W/BK) on the ERC, or at J300 pins 1 to 2 on the machine control board. A working sensor reads approximately 1080-1100 ohms at room temperature. If resistance is out of range, check the wiring harness and connectors first, then replace the upper oven sensor if the wiring is intact. If resistance tests normal at the board connectors, the control board itself may need replacement.

If the upper oven sensor is the cause, sensor replacement parts typically range from $20 to $60 depending on the model, and the repair is manageable for most DIYers since it involves removing a few screws and a connector. If the wiring harness or a connector is the issue, cost is minimal and may require no parts at all. A control board replacement is the most expensive outcome, with parts running $150 to $350 or more. Professional labor adds $100 to $200 on top of parts.