Samsung Oven Error C-21 – Oven Overheating / Temperature Sensor Error
The Samsung range sensed too high an oven temperature – real overheating or a bad sensor reading.
Unverified: this manufacturer-specific definition comes from a single source or varies by model. Confirm it with a brand-specific scan tool.
Safety first · Consult a professional
If the oven keeps heating with the controls off, switch off its breaker immediately – that's a stuck relay and a fire risk. On a gas range, don't touch gas parts; if you smell gas, leave the house and call 911 or your gas utility from outside.
- Unplug the appliance or switch off the breaker before opening any panel. Mains voltage can kill.
- Hot surfaces and hot water can cause burns. Let the appliance cool down first.
At a glance
Severity: High
- Meaning
- Oven Overheating / Temperature Sensor Error
- System
- Samsung · Oven / Range
- Typical repair cost
- $0–$600
- DIY difficulty
- Moderate
On Samsung ranges and wall ovens sold in the US, C-21 is reported as an overheating code: the temperature sensor tells the control the cavity is hotter than it should be, and the oven shuts the heat off. Samsung's own information-code tables group C-20 through C-23 more generally as sensor malfunctions, so the exact trigger isn't officially spelled out and can vary by model. In practice, the two branches are very different: either the oven really is overheating because a relay on the control board won't let go, or the sensor or its connector is feeding the control a false high reading. Telling these apart with an oven thermometer is the first job before any part is ordered.
How it looks on the display
Model families & display variants
| Model family | Shows | Note |
|---|---|---|
| Samsung freestanding and slide-in ranges | C-21 | Typically reported with overheating during bake, broil or self clean. |
| Samsung Flex Duo / dual-oven ranges | C-21 | Can involve the upper or lower cavity sensor; check which oven was running. |
| Related sensor codes | C-20 | Samsung lists C-20 to C-23 as sensor malfunctions; the numbers point to different sensors depending on model. |
Symptoms
- C-21 on the display during baking, broiling or self clean
- Oven gets far hotter than the set temperature, food burns
- Heat stays on even after pressing OFF/CLEAR
- C-21 appears as soon as the oven is switched on while cold
- Cooling fan runs hard and the front feels unusually hot
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Relay on the main control board stuck closed – oven heats without control
- Oven temperature sensor out of spec or its connector damaged
- Grease fire or heavy residue during broil or self clean
- Cooling fan not running (slide-in and wall ovens)
- Sensor wiring chafed or burned near the cavity wall
Fix it step by step
Stop the heat
Press OFF/CLEAR. If the elements keep glowing or the oven keeps getting hotter, switch off the range's breaker right away and keep the door closed until it cools.
Power-cycle the range
Once cool, disconnect power for at least 30 seconds – Samsung's own reset – by unplugging the range or turning off its breaker, then restore power and clear the display.
Thermometer check
Put an oven thermometer on the middle rack and bake at 350°F for 30 minutes. A reading far above 350°F means real overheating (control/relay); a normal reading with C-21 points to the sensor.
Inspect the sensor
With the power off, look at the sensor probe on the upper rear wall. A bent probe, a loose mounting screw or scorched wiring at the connector can cause false high readings.
Tools: Flashlight, Screwdriver
Measure resistance
A technician – or an experienced DIYer with power off – unplugs the sensor and measures it: around 1,000 to 1,100 ohms at room temperature is normal for these RTD probes. A reading far off, or one that jumps when the wire is flexed, means a new sensor.
Tools: Multimeter
Check the cooling fan
On slide-in and wall ovens, listen for the cooling fan when the oven heats. A silent fan lets the controls and door area overheat and should be replaced.
How to reset C-21
- Press OFF/CLEAR and let the oven cool completely
- Cut power for at least 30 seconds at the plug or breaker
- Restore power and verify temperature with an oven thermometer
Where the parts are
- 1Oven temperature sensor
- 2Heating element
- 3Fan
- 4Door switch
- 5Gas valve
- 6Temperature sensor
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Power reset and cleaning residue | Yes | $0 |
| Oven temperature sensor replaced | Yes | $120–$260 |
| Technician diagnosis | No | $100–$180 |
| Main control board replaced | No | $300–$600 |
| Cooling fan motor replaced | No | $180–$350 |
Rough US estimates; technician call-out fees vary by region. Not a quote.
When to call a technician
Call Samsung service or an appliance technician right away if the oven kept heating with the controls off or the thermometer test shows it running far above the set temperature. Don't use the range until the control board is fixed; a sensor-only fault is less urgent but should be repaired before the next self clean.
Frequently asked questions
Is C-21 dangerous?
It can be. If the oven really overheats because a relay is stuck, it's a fire risk. If it's just a bad sensor reading, the oven shuts off early, which is annoying but safe.
Why does C-21 show up during self clean?
Self clean runs close to the oven's maximum temperature, so any extra heat from residue or a slow cooling fan can push it over the limit.
Will a new sensor fix C-21?
Only if the sensor or its connector is the cause. If the thermometer shows the oven genuinely overheating, the control board is the likelier culprit.
Can I keep using the cooktop?
Usually yes, since the burners are controlled separately, but if the oven kept heating with controls off, leave the breaker off until it's repaired.
Sources
- Official Samsung user documentation and support pages (facts only; wording is our own)
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