That musty smell comes from mold and bacteria feeding on detergent and fabric softener residue in damp spots: the front-load door gasket, the dispenser, the drain pump filter and the outer tub. Clean the gasket and run a tub clean cycle with bleach or a washer cleaner, then leave the door open between loads.
Where the smell comes from
High-efficiency washers use very little water, and front-loaders seal tightly. That's good for your water bill and bad for odor. Detergent that doesn't fully dissolve, especially in cold washes, coats the outer tub you never see. Fabric softener adds its own residue on top. Lint, hair and a bit of standing water finish the job, and mold grows in the dark.
Front-loaders get it worst because of the rubber door gasket and the airtight door. Top-loaders aren't immune, though: residue collects under the agitator or impeller and on the outside of the wash basket.
A sewer smell is a different problem. If it's coming from the standpipe or a floor drain, it's a plumbing issue, and a plumber should look at it.
1. Clean the door gasket (front-loaders)
Pull back the folds of the rubber boot and look, especially at the bottom around the six o'clock position. You'll often find hair, a sock, coins, slimy gray film or black spots. On a front-loader, that's very often where the smell starts.
LG's own instructions call for an oxygen bleach solution at about 5 g per 5 L of warm water (roughly a teaspoon in a gallon and a third), scrubbed into the gasket with gloves on, then wiped dry. Do it at least monthly.
Unplug the washer and put on rubber gloves.
Pick out anything caught in the folds, including the small drain holes at the bottom of the boot.
Scrub every fold with the diluted oxygen bleach and an old toothbrush or a soft cloth.
Wipe the gasket and the door glass dry with a towel and leave the door open until it's fully dry.
2. Run a tub clean cycle
Most current washers have a cycle built for this: Tub Clean on LG (the tCL message is its reminder), Clean Washer on Whirlpool and Maytag, and similar names on other brands. It's meant to run with an empty drum and a cleaner, and it reaches residue that normal wash cycles leave behind.
Run it empty, with a washer cleaner tablet or the amount of liquid chlorine bleach your manual gives. Whirlpool says not to use thickened, easy-pour or no-splash bleach in this cycle. Both Whirlpool and LG suggest doing it once a month. If a cycle reports items in the drum (Whirlpool F0E1, Maytag rL), take everything out and start again.
If there's no dedicated cycle, run the hottest, longest wash your machine offers with the same cleaner and nothing else in the drum.
3. Clean the detergent dispenser
Pull the drawer all the way out. Most have a release tab in the softener section. Soak it in hot water, scrub the channels with a brush, and wipe out the cavity it slides into, where black mold often grows on the ceiling. On top-loaders, lift out any removable cups and clean them the same way.
Give it a minute or two every time you clean the gasket. A drawer that stays damp between loads grows mold, and whatever grows there gets rinsed into your next load.
4. Clean the drain pump filter
Water sitting behind a clogged pump filter goes stale fast, and LG lists a blocked filter as a cause of odor for exactly that reason. On front-loaders, open the small panel at the bottom front, drain the trapped water into a pan, and twist out the filter to clean it. See our step-by-step guide to cleaning the washer drain pump filter for the details.
5. Change how you wash
Cleaning gets rid of the smell. Habits keep it away.
Use HE detergent and measure it. Extra soap just leaves extra residue behind. If you wash mostly in cold water, run a warm or hot load now and then so detergent can dissolve and flush out. Go easy on liquid fabric softener, or skip it.
Take clothes out as soon as the cycle ends. Whirlpool warns that wet clothes left sitting in the washer can mildew, and they keep the drum damp too. After the last load of the day, leave the door and the dispenser drawer slightly open so the inside can dry. Whirlpool and LG both recommend it, and it costs nothing. Keep kids and pets away from an open front-loader.
If the smell won't go away
Repeat the gasket clean and two tub clean cycles back to back. If the odor survives that, residue may be caked on the outer tub or the internal drain hose where only disassembly can reach it, or the gasket may be permanently stained and need replacing. LG's guidance is to book service when odor continues after repeated tub cleans.
When to call a professional
A technician should look at it if the smell continues after several tub clean cycles and a full gasket and filter clean, or if the gasket is torn. For a sewage smell from the standpipe or floor drain, call a plumber, because that smell comes from the house drain.