Seeing **C-21** on a Samsung microwave narrows the problem to **temperature sensor error**. What you do next depends on whether the code is an issue, a normal status/test message, or a model-dependent interpretation. Samsung uses overlapping code conventions across model years and regions. This page keeps the appliance context attached to the code so a same-looking string from another product family is not misapplied. The recorded display form is **C-21**. Search normalization stores it as **C21** while preserving the characters a homeowner actually sees.
Reviewed by Ethan Mercer · Last reviewed August 17, 2026
Written by
Ethan Mercer Appliance Repair Content SpecialistPublished August 17, 2026Updated August 22, 2026Technically reviewed August 17, 2026
Content status:
Verified
Error codeC21
ApplianceMicrowave
Quick answer
Temperature sensor error.
Model compatibility: Samsung can reuse or reformat codes across series and model years, so C21 may mean something different on another appliance or generation. Confirm this against your model’s documentation and record your full model number before acting.
Plain language
What this code means
Seeing **C-21** on a Samsung microwave narrows the problem to **temperature sensor error**. What you do next depends on whether the code is an issue, a normal status/test message, or a model-dependent interpretation. Samsung uses overlapping code conventions across model years and regions. This page keeps the appliance context attached to the code so a same-looking string from another product family is not misapplied. The recorded display form is **C-21**. Search normalization stores it as **C21** while preserving the characters a homeowner actually sees.
Signs
Symptoms you may notice
When the C-21 condition is present, the control may stop or limit operation because a temperature reading is missing or implausible.
Depending on the exact model, heating, cooling, drying, or defrost behavior can become inconsistent.
A symptom that fits C-21 is that the display may return at a similar stage each time the affected sensor is checked.
A symptom that fits C-21 is that c-21 appears and the microwave can stop or limit the function associated with temperature sensor error.
Why it happens
Possible causes
varies by model/region — cross-region baseline — Temperature sensor error
Before you call
Safe checks you can make
These are simple, non-hazardous checks only. If anything is unclear, stop and contact a technician.
A safe owner-level check is to record when the code appears and whether the appliance had just heated, cooled, or defrosted.
Before opening any service area, confirm vents, doors, filters, and ambient conditions are normal where they affect the sensor reading.
Before requesting service for C-21, use the exact model manual before assuming the sensor itself is defective.
Before requesting service for C-21, record the exact code and model number.
The next non-invasive check is to power the microwave off for 60 seconds only if Samsung's model guidance allows a reset.
The next non-invasive check is to do not remove the outer cabinet or access internal high-voltage components.
Important safety warning. Safety takes priority over clearing C-21. Do not remove the microwave outer cabinet. High-voltage components can retain dangerous energy even after the appliance is unplugged.
Get help
When to request repair service
For C-21, the service threshold is straightforward: Persistent temperature-sensor codes usually require resistance/connection checks at the sensor, harness, and control—work best done with the model-specific service procedure. Bring the exact model number and a photo of the display so the diagnosis stays tied to the documented Samsung code.
Book your repair
Seeing this code on your Samsung appliance?
Book a specialist visit for a clear estimate and approval before any repair.
You can try the one reset Samsung documents for the model, but **C-21** returning afterward means the condition still exists. Note the operating stage instead of cycling power repeatedly.
Continue only if the appliance is otherwise safe and the owner-level checks are appropriate. Stop for leakage near electrical parts, smoke, burning odor, arcing, gas concerns, repeated breaker trips, uncontrolled heating, or unsafe temperatures.
Not automatically. Samsung error codes are diagnostic indicators, not part numbers. Confirm the circuit around **C-21** before replacing anything.
The same-looking code can be reused on another Samsung appliance family or reformatted by region/model year. Match the appliance type and exact model before applying a meaning. This page therefore keeps **Microwave C-21** separate from same-looking codes used by other Samsung appliance families.
