Sub-Zero Classic BI and Designer Code 20-2-00: defrost heater circuit open

What 20-2-00 means

Classic Built-In units such as the BI-36U/S and Designer models like the DET3050CI display 20-2-00 when the defrost circuit on the freezer side is open. Classic BI lists it as the freezer defrost heater open; Designer calls it the Zone 2 defrost heater open. On both, the defrost bimetal may be stuck open. Defrost cannot melt ice from the coil, so frost builds behind the panel and the freezer gradually loses cold.

Common causes of 20-2-00

A defrost bimetal stuck open
An open defrost heater
A broken connection in the defrost circuit

✓ One safe check you can try

1. Check the freezer or Zone 2 rear panel for frost. 2. Keep the door closed to slow ice growth. 3. Reset the breaker once. 4. Use a thermometer; move food if the freezer rises above zero degrees. 5. Do not scrape the coil cover.

! Why to stop there

The heater and bimetal sit on the coil behind the freezer panel
Scraping ice can damage refrigerant tubing
Testing the defrost circuit requires access near line voltage

Opening a panel yourself does not automatically cancel a manufacturer warranty, but it can cause accidental damage, and some manufacturers set their own service conditions. Check your warranty terms, or ask us, before deciding.

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Other Refrigerator codes

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20-2-0020-2-00 questions

What is a defrost bimetal?

It is a small temperature switch on the defrost circuit. When stuck open, it stops power reaching the heater. 20-2-00 can point to it or to the heater itself.

Why is my freezer frosting up?

Without defrost, ice builds on the coil and blocks airflow. The freezer then loses cold over several days. We melt the ice and restore the circuit.

Why does my Designer say Zone 2 instead of freezer?

Designer models number their compartments, and this code names the defrost heater in Zone 2. The Classic BI simply labels it the freezer defrost heater. The open circuit, and the way we test it, are the same.