If a Samsung front-loader smells, the cause is almost always biofilm in the door gasket and the detergent drawer, not the drum. Running Self Clean on its own will not fix it - the gasket has to be wiped out by hand first.
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Here is what actually causes the smell, and the order that clears it for good rather than for a week.
Why front-loaders smell and top-loaders mostly do not
A front-loader seals against a flexible rubber gasket, and that gasket has a fold in it that holds water after every wash. Warm, damp, dark and fed by detergent residue, it grows a black biofilm. Front-loaders also use far less water than top-loaders, so less residue gets rinsed away.
Two habits make it worse: too much detergent, and non-HE detergent in an HE machine. Both leave surplus surfactant behind that never rinses out, and that residue is what the biofilm feeds on.
Clean it in this order
Step 1: The gasket, by hand
This is the step people skip, and it is the one that matters. Pull the rubber fold back and wipe inside it with a cloth and a dilute bleach solution or white vinegar. Expect black residue and expect it to be unpleasant. Work the whole way round, including the bottom where water collects. Dry it when you are done.
Step 2: The detergent drawer
Remove it completely - most pull out and release with a catch at the back. Wash the drawer and the softener insert in hot water, and clean the housing it slides into, which grows the same film.
Step 3: The drain pump filter
Behind a small access panel at the bottom front. Put a towel and a shallow tray down first, because water will come out. Unscrew the filter, clear the lint, coins and hair, and rinse it. A partly blocked filter leaves standing water in the machine permanently, which will reseed the smell no matter how well you clean everything else.
Step 4: Now run Self Clean
With the gasket, drawer and filter clean, run Self Clean or Pure Cycle on an empty drum. Add nothing - no detergent, no bleach unless the manual for your model calls for it. The cycle runs hot with a high water level to flush the drum and tub. On most Samsung models it takes two to four hours.
Keeping it from coming back
Leave the door ajar between washes so the gasket dries. Pull the detergent drawer open slightly for the same reason. Use the HE detergent your machine calls for, and use less than you think - the marked line on the cap is generous. Wipe the gasket dry occasionally. Run Self Clean monthly, which most Samsung models will prompt you to do.
What a smell is not
A musty smell is a cleaning problem. A burning smell is not, and it is worth being clear about the difference. Burning rubber or hot electrical smells during a cycle mean a failing drive belt, a seized bearing or a motor fault, and running the machine again to see if it repeats is the wrong response. Stop and have it looked at.
Frequently Asked Questions
Can I use bleach in the Self Clean cycle?
Check your manual. Some Samsung models permit a small amount in the bleach dispenser, others specifically say to run it empty. Bleach does not reach inside the gasket fold in any case, which is where the problem lives.
How often should I run Self Clean?
Monthly, or whenever the machine prompts. If you wash mostly cold, err toward more often - cold cycles leave more residue behind than warm ones.
The smell came back within a week. What did I miss?
Almost always the drain pump filter or the gasket fold. If both are genuinely clean and the smell returns quickly, there may be standing water in the tub from a partial drain fault, which is a repair rather than a cleaning issue.
When to call
If the smell survives a proper clean, or you have standing water, a burning smell or a machine that will not drain fully, book a washing machine repair. The $100 diagnostic comes off your repair labour.