Samsung Range Error Code C-21

The C-21 error code on a Samsung range signals an abnormal temperature condition in the oven cavity, the main PCB temperature circuit, or both. Specifically, the control board has detected that either the oven temperature has climbed to an unsafe level, or the temperature sensor circuit feeding the main PCB is open or shorted. The oven temperature sensor (also called an RTD sensor) is the primary monitoring component here. At room temperature, a properly functioning sensor will read approximately 1080 ohms of resistance. A reading significantly above or below that value indicates a failed sensor, which can cause the board to misread oven temperatures and trigger the C-21 fault.

The heating elements themselves are also suspects. If a broil, bake, or convection heater develops a short or is drawing excessive current, it can cause the oven cavity temperature to climb beyond safe operating limits. Similarly, if the relays controlling those heaters on the main PCB stick in a closed position, a heater may continue to run even when the control board commands it to shut off, resulting in uncontrolled temperature rise. The DLB (Double Line Break) relay is particularly important to check, as it is part of the safety interlock for the heating circuit.

When diagnosing C-21, always begin by disconnecting power before taking any resistance measurements. Check the oven sensor resistance, verify heater element resistance values for continuity and shorts to ground, and inspect the broil, bake, and convection relays on the main PCB for signs of welding or failure. If all components test within spec, the main PCB itself may be the source of the fault.