Sub-Zero error codes EC 20 and EC 21 relate to the freezer temperature and defrost system. EC 20 suggests that the defrost is under-heated, while EC 21 means the defrost system isn’t working correctly and the temperature is too high.

• Manual Defrosting: If you notice ice buildup on the evaporator coils, it’s important to manually defrost the freezer. To do this, turn off the refrigerator and leave the freezer door open until the ice has melted completely. This can temporarily resolve the issue.

• Inspect the Defrost Heater: If you have the necessary skills and tools, inspect the defrost thermostat, defrost heater, and defrost control board for visible issues. Replace any components that appear faulty.

There are several potential causes for these Sub-Zero error codes. Many things can go wrong, from issues with wiring to the freezer evaporator. The best way to troubleshoot this problem is to call a Sub-Zero error codes repair expert for help. EC 24 is also related to the defrost.