Samsung Microwave Error Code C-21

C-21 means the microwave's internal cavity temperature sensor has reported a value outside the valid range, specifically below -5°C or above 250°C. The control board treats this as an open or short circuit condition in the sensor. As a safety response, the unit enters cancel mode and stops operating. The sensor, its wiring, and the connector to the PCB all need to be inspected.

No. When C-21 is triggered, the microwave enters cancel mode and will not operate normally, which is the intended protective behavior. Attempting to bypass or ignore the code without resolving the underlying sensor fault is not recommended. The temperature sensor is part of the system that prevents the cavity from reaching unsafe temperatures.

If only a connector needs to be reseated, there may be no parts cost, though a technician labor fee could range from roughly $75 to $150 depending on location. If the temperature sensor itself needs replacement, parts and labor combined typically range from $100 to $250. If the PCB is at fault, costs can be higher, and it may be worth comparing repair cost against the value of the appliance.

Some causes of C-21, such as a loose wiring connector, can be addressed without replacing any parts if you are comfortable working inside the appliance. However, microwave interiors can retain lethal high-voltage charge in the capacitor even when unplugged, so the repair should only be attempted by someone familiar with high-voltage safety procedures. If the sensor itself has failed, it will need to be replaced. If you are unsure, a qualified appliance technician should perform the diagnosis.

Unplugging the microwave and restoring power may temporarily clear the display, but C-21 will return if the underlying fault with the temperature sensor or its wiring has not been corrected. A reset does not repair a failed sensor or a broken connection. The fault condition must be physically resolved for the code to stay clear.