Sub-Zero Classic BI and Designer Code 15-4-01: defrost relay will not release

What 15-4-01 means

Classic Built-In models like the BI-36UFD/S and Designer units such as the DEC3050R display 15-4-01 when the defrost relay is stuck closed. Designer lists it as the Zone 4 relay. A closed relay keeps power flowing to the defrost heater when the board wants it off. The coil that should be cooling is being warmed instead, so the freezer or zone loses cold quickly, and you may notice water dripping or unusual warmth inside.

Common causes of 15-4-01

Relay contacts welded shut on the control board
A board output stuck on
A wiring problem that keeps the defrost circuit powered

✓ One safe check you can try

1. Check the freezer temperature right away with a thermometer. 2. If it is rising, move frozen food to another freezer or a cooler with ice. 3. Turn the breaker off if the inside is getting warm, and leave it off until we arrive. 4. Place towels where water drips.

! Why to stop there

A heater left on can overheat nearby plastic parts
Relay contacts on the board need testing with power applied
The board may need replacing, which requires correct programming

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

80Sub-Zero 700TF Code 80: No inverter feedback after a board change ddSub-Zero 600 and 700 Series Display dd: Diagnostics switched off deSub-Zero 600 and 700 Series Display de: Diagnostics enabled 23Sub-Zero 600, 700 and 648PRO Code 23: Defrost overheat with no feedback 50Sub-Zero 600 and 700 Series Code 50: Refrigerator compressor running too long 41Sub-Zero 648PRO Code 41: Zone compressor or wiring problem 81Sub-Zero 700-2 Code 81: Variable-Speed compressor fails to start 82Sub-Zero 700-2 Code 82: VS compressor controller needs replacement

15-4-0115-4-01 questions

Is 15-4-01 urgent?

Yes. The defrost heater stays powered, so the coil warms when it should cool. Food can thaw within hours. Move it out and call us; switching the breaker off stops the heater for now.

Is 15-4-01 worse than 15-4-00?

15-4-00 is the relay stuck open, so defrost never runs and frost builds. 15-4-01 is stuck closed, so defrost never stops. The second one warms the unit much faster.

What will the repair involve?

We confirm the relay state, check the defrost heater and wiring for heat damage, and fix the board side. You get a written price first and a 30-day workmanship warranty.