Sub-Zero UC-24 Code 23: defrost overheat without feedback

What 23 means

Code 23 appears on legacy UC-24 undercounter models like the UC-24C and UC-24F when the control sees a defrost overheat together with no voltage feedback on the gray/white wire at defrost start. Put simply, the defrost circuit did not report in, and the control also judged that defrost ran too hot. That number turns up on full-size 600/700 models too, but with their own list rather than this one. You may notice frost patterns that come and go, water on the cabinet floor, or uneven temperatures.

Common causes of 23

An open or intermittent gray/white feedback wire
A defrost terminator that does not open on time
A defrost heater circuit wired or connected incorrectly
A control board that misreads the defrost feedback

✓ One safe check you can try

1. Check the cabinet floor for water and wipe it dry. 2. See whether the drain area under the unit is clear. 3. Close the door firmly and check the seal. 4. Reset power at the breaker once, after one minute off. 5. If 23 returns, stop using the unit for sensitive items and call us.

! Why to stop there

Overheating defrost parts can warp the liner if handled wrong
The heater circuit runs on line voltage behind the rear cover
Feedback and overheat checks need a meter and an observed defrost cycle

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.

→Same appliance

Other Undercounter & Drawers codes

Service flashingSub-Zero UC-24 Undercounter "Service" Flashing: excessive compressor run 05Sub-Zero UC-24 Code 05: refrigerator cabinet sensor reading 06Sub-Zero UC-24 Code 06: refrigerator evaporator sensor issue 07Sub-Zero UC-24 Code 07: freezer cabinet thermistor reading 08Sub-Zero UC-24 Code 08: freezer evaporator thermistor 22Sub-Zero UC-24 Code 22: no defrost voltage feedback 50Sub-Zero UC-24 Code 50: refrigerator compressor runs too long 21Sub-Zero UC-24 Undercounter Code 21: defrost overheat

2323 questions

How is code 23 different from code 22 on a UC-24?

Both involve missing voltage feedback on the gray/white wire at defrost start. Code 23 adds a defrost overheat, so we check the parts that end defrost as well as the feedback wire.

Is there a fire risk?

The unit has safeties, but an overheating defrost circuit should not be ignored. If you smell burning plastic, switch the breaker off and call us.

What happens during the service call?

We run a controlled defrost, check the heater, terminator and wiring, and confirm feedback reaches the control. You approve a written price first, and the work carries a 30-day workmanship warranty.