--- title: "Sub-Zero code 21: the defrost cycle got too hot" description: "What 21 means on Sub-Zero code 21: the defrost cycle got too hots, what to check before booking, and when it is not a failure at all." url: "https://freezerrepair.center/error-codes/sub-zero-21/" --- # Sub-Zero code 21: the defrost cycle got too hot On IC-27 integrated columns and 700 Series models, 21 is the code Sub-Zero gives for defrost overheat. ## What 21 actually means. On IC-27 integrated columns and 700 Series models, 21 is the code Sub-Zero gives for defrost overheat. The defrost heater warms the evaporator to melt frost, and the control expects it to stop within limits; this code says it did not. Sub-Zero freezer display What to do when 21 shows on the freezer ### Kind of code Defrost system A frost-free freezer warms its coil for a few minutes several times a day to melt the frost, and the control noticed that this did not happen or took too long. A heater that burned open, a defrost thermostat or a timer that stuck, or a drain frozen shut lets frost wrap the coil until air cannot pass. Chest freezers without automatic defrost do not show these codes; their frost comes off by hand. ### Usually leads to Freezer defrost system repair Repairing the heater, the defrost thermostat or sensor and the timer or board that keep ice off the hidden coil in a frost-free upright, column or undercounter freezer. ### Shows up as Freezer Error Code A freezer error code appears on the display: letters and digits, a flashing temperature, or a warning symbol, sometimes with an alarm and sometimes with the freezer still running. ### Make Sub-Zero Sub-Zero freezers repaired in the home, with the food kept shut in while the cause is found. ### Source Sub-Zero answer: IC-27 integrated columns error code 21 IC-27 integrated columns and 700 Series (shown as 21). 700 Series owners get no troubleshooting step for this code from Sub-Zero. ## Before you book, in this order. Each step comes from Sub-Zero's own guidance for 21 on its freezers. Follow it to the end: the last card says whether this is a visit. 01 On an IC-27 column, switch the breaker off for 30 seconds and back on, then see whether 21 returns after the next defrost. 02 Check that frozen food is still solid and that no burning or hot plastic smell comes from the freezer. 03 If 21 comes back or you notice a burning smell, turn the breaker off and book a visit. ### Still there? It usually turns into [freezer defrost system repair](https://freezerrepair.center/services/defrost-system-repair/). Book with the code and the model number. ### What not to do Code 21 does not mean the freezer is short on cooling. It is about the heater side of defrost, while 24 reports the opposite problem, a defrost that stays too cool. ## What you may notice with it. The freezer problems 21 tends to arrive with. Answer these at the freezer before anyone is booked. [All problems](https://freezerrepair.center/problems/) Before you call ### [Freezer Error Code](https://freezerrepair.center/problems/freezer-error-code/) [All 7 causes, cheapest first](https://freezerrepair.center/problems/freezer-error-code/) It also comes with - [**Heavy Frost Buildup in the Freezer**](https://freezerrepair.center/problems/freezer-frost-buildup/) - [**Burning Smell Near the Freezer**](https://freezerrepair.center/problems/freezer-burning-smell/) Problem ### Freezer Error Code 7 causes, cheapest first Where 21 usually leads ## Freezer defrost system repair. **Defrost heater, defrost thermostat or timer · low to moderate.** Book a visit [What the job involves](https://freezerrepair.center/services/defrost-system-repair/) ## Sub-Zero freezers. Sub-Zero freezers repaired in the home, with the food kept shut in while the cause is found. [Sub-Zero freezer repair](https://freezerrepair.center/brands/sub-zero/) More Sub-Zero codes [EC07](https://freezerrepair.center/error-codes/sub-zero-ec07/) [EC08](https://freezerrepair.center/error-codes/sub-zero-ec08/) [EC40](https://freezerrepair.center/error-codes/sub-zero-ec40/) [22](https://freezerrepair.center/error-codes/sub-zero-22/) [24](https://freezerrepair.center/error-codes/sub-zero-24/) [20 4 50](https://freezerrepair.center/error-codes/sub-zero-20-4-50/) [95 1 00](https://freezerrepair.center/error-codes/sub-zero-95-1-00/) [35 C 00](https://freezerrepair.center/error-codes/sub-zero-35-c-00/) [90 5 80](https://freezerrepair.center/error-codes/sub-zero-90-5-80/) Defrost system on other makes [Fisher & Paykel F2](https://freezerrepair.center/error-codes/fisher-and-paykel-f2/) [Marvel Ed](https://freezerrepair.center/error-codes/marvel-ed/) [Perlick TEL](https://freezerrepair.center/error-codes/perlick-tel/) [All 6 codes of this kind](https://freezerrepair.center/error-codes/#family-defrost) Sub-Zero builds this ### Freezer column A built-in, full-height freezer that stands alone in the cabinetry, often beside a matching fresh-food column, with a stainless or panel-ready door and an electronic control. Sub-Zero builds this ### Undercounter freezer A 15- to 24-inch freezer or a pair of freezer drawers built in under a counter, in a kitchen island, a home bar, a basement or a pool house, venting from the front. ## In Sub-Zero's own words > Defrost overheat [Sub-Zero answer: IC-27 integrated columns error code 21](https://www.subzero-wolf.com/assistance/answers/sub-zero/ic-27-integrated-columns/ic-27-integrated-columns-series-error-code-21) [Sub-Zero answer: 700 Series error code 21](https://www.subzero-wolf.com/assistance/answers/sub-zero/700-series/700-series-error-code-21) Every code on this site is taken from the manufacturer's documentation, never from a forum or a parts listing. IC-27 integrated columns and 700 Series (shown as 21). 700 Series owners get no troubleshooting step for this code from Sub-Zero. ## Sub-Zero 21 freezer repair, where we come out. The same visit in every metro below: the code, the model number, and a diagnosis before any part is ordered. 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On an IC-27 column, switch the breaker off for 30 seconds and back on, then see whether 21 returns after the next defrost. If it comes back, it needs a visit. ### Is Sub-Zero code 21 a fire risk? The control flags overheat so the heater does not keep running unchecked. If you smell burning, cut power at the breaker and keep it off until a technician has checked the heater, the limit and the wiring. ### Will a breaker reset fix code 21 on an IC-27 column? Sub-Zero suggests it as the first step, and a one-time glitch may not return. If 21 appears again after the next defrost, the part that ends the heater cycle needs testing. ### Does code 21 mean my Sub-Zero freezer will stop defrosting? Not necessarily right away, but a defrost circuit that overheats is not working as designed. Over time you may see frost on the back panel, so book a visit if the code repeats. --- **[Read on the site: Sub-Zero code 21: the defrost cycle got too hot](https://freezerrepair.center/error-codes/sub-zero-21/)** **[Book a visit with FreezerRepair.center](https://freezerrepair.center/schedule/)**