Samsung C-21 fault codewhat it means and how to fix it
The cavity temperature has gone over the limit during operation. Samsung annotate this one "(Fire sensed.)", which is their wording and worth taking at face value.
Take care
What C-21 means
Samsung describe C-21 as appearing when the microwave temperature is high — specifically, where the temperature rises over the limit temperature during the operation of each mode — and they add a two-word parenthesis that no other code on their list carries: fire sensed. That is Samsung’s wording, not an interpretation of it, and it is the reason this page is rated more seriously than an overheat message would otherwise be. Their action is to unplug the power cord, wait long enough for it to cool, and then restart the microwave, which is a recovery rather than a service call, so they are not saying the appliance is destroyed.
What they are saying is that the appliance detected a temperature it is designed to treat as a fire risk and shut down. Two very different situations produce this. The mundane one is heat: a long grill or convection run, a cavity that was already warm, or restricted ventilation, and the appliance protecting itself with nothing actually burning. The one that matters is food. A microwave will readily set fire to something left running too long — popcorn is the classic, but anything dry and starchy will do it, and so will a paper bag or a plastic tray.
So the first thing to do is not to reset anything but to look at what is in the cavity, and if there is smoke or flame the answer is the opposite of the instinct: keep the door shut and pull the plug. Opening the door feeds a cavity fire the air it is short of. If the appliance recovers, cools and works normally afterwards with nothing scorched, treat it as protection working. If it returns without an obvious heat source, the temperature sensing itself is suspect and that is a service matter.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Food burning or on fire in the cavity | The situation Samsung’s parenthetical points at. Dry starchy items and packaging are what ignite in practice. | Common |
| Long grill or convection run | Combination modes put real oven heat into the cavity, and the limit applies during the operation of each mode. | Common |
| Ventilation restricted | Heat that cannot leave the appliance keeps the cavity climbing towards the threshold on an ordinary cycle. | Occasional |
| Temperature sensor reading incorrectly | The case where nothing was hot. Samsung give the open or short sensor its own code, C-20, with no owner action on their UK page. | Occasional |
What to try yourself
Look through the door before you open it. If there is smoke or any flame inside, keep the door closed.
A fire in the cavity is starved by keeping the door shut and fed by opening it. Pull the plug rather than opening up to look.Unplug it. This is Samsung’s own first step and it is also how you stop the appliance restarting while you deal with the rest.
Let it cool properly. Samsung’s wording is to wait long enough for it to cool, and that wait is the actual remedy rather than the unplugging.
Once cool, open up and look at what was inside and at the cavity itself. Scorching, a melted tray or a burnt paper bag tells you this was the food rather than the appliance.
Clean the cavity, check the vents are clear, and restart it. If the code comes back with nothing hot in it and good ventilation, stop using it and get the temperature sensing checked.
Get a qualified appliance engineer to look at your Samsung C-21
We do not pass enquiries to a repair firm, so there is no form here. When you book a qualified appliance engineer, tell them the make, the model and the exact code or message on the display, and ask whether they carry parts for this make — that is what turns one visit into a repair rather than a quote.
What it costs to fix
Typical repair cost
£0–£140
Time on site
30 minutes
Nothing if it was food or heat and the appliance recovers. If the sensing is at fault, a sensor with a visit is typically £80 to £140, and a fire-damaged cavity is usually a replacement rather than a repair.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Own this appliance and had this code? . Nothing is published until a person has read it.
Related Samsung fault codes
- C-20Get it checkedThe temperature sensor circuit is open or short. Samsung’s UK page gives no owner action — unplug it and call them — though their combination manual allows one retry first.Related: overheating and cooling
- C-d0Usually simple to fixA touch key has been held for more than ten seconds. Usually moisture or dust on the panel, and Samsung ask you to clean the button.Related: same brand
- C-F0Get it checkedThe two processors inside have stopped talking to each other. Samsung publish no owner remedy — unplug it and contact them.Related: same brand
- C-F2Usually simple to fixAbnormal communication on the touch key. The only one of Samsung’s six codes with a one-button remedy: press Stop and try again.Related: same brand
- C-F1Get it checkedThe appliance cannot read or write its own memory. Published in Samsung’s combination-model manuals and absent from their support page.Related: same brand
- C-A1Get it checkedThe vent damper has not been sensed opening or closing within a minute. A code only the over-the-range models can show.Related: same brand
Own a Samsung microwave? Save it and its codes come first next time.
Related guides
Common questions about Samsung C-21
Samsung say "Fire sensed". Was there actually a fire?
Not necessarily, and we are not going to tell you there was. That parenthesis is Samsung’s own annotation on a high-temperature code, and the threshold can be reached by heat alone. It is a strong hint about how they classify the condition, which is why looking in the cavity comes before resetting anything.
Can I use it again after it cools?
Samsung’s published action ends with restarting the microwave, so yes, provided it recovers and behaves normally and you can see what caused the heat. What is not reasonable is repeatedly resetting it when the code returns with nothing hot inside — at that point the sensing rather than the food is in question.
How is this different from C-20?
C-20 is the temperature sensor being open or short — the sensing circuit itself broken — and Samsung’s UK page gives it no owner action at all, only unplug and contact them (their combination manual allows one Stop/Eco retry). C-21 is a real temperature reading above the limit, and it is one of the two codes on their UK list where they do give you something to do.
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer support portal
- Manufacturer technical and service documentation
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.