Odor in a Bosch WAT28400UC is dealt with by the maintenance the manual describes. Run the Drum Clean program (Bosch recommends it before the first load, after 1 to 2 tablespoons of detergent in the main-wash chamber II) to clean the system, and use it as a routine. Clean the detergent dispenser tray, wipe the housing and control panel with hot soapy water or a mild non-abrasive cleanser, and check the drum after each load for debris. If descaling becomes necessary, follow the maker's instructions; Bosch says descaling is not necessary when correct amounts of detergent are used. Excess detergent and non-HE detergent leave suds and residue that smell.
Differential
Likely causes of “Bosch 300 Series WAT28400 front-load washer smells musty, sour or like mildew”, and how to tell them apart
- 1
Residue in the detergent dispenser
What separates it There is a sour smell near the tray because of residue in the detergent dispenser
How to confirm Clean the insert and tray under warm running water
- 2
Too much or non-HE detergent
What separates it There are suds, residue and odor because too much or non HE detergent was used
How to confirm Use less HE detergent, and measure it for the load
- 3
Debris and lint in the drum or pump
What separates it There is a musty smell because of debris and lint in the drum or the pump
How to confirm Check the drum after each load; clean the pump
- 4
Water left in the system
What separates it There is a stale smell because water is left in the system
How to confirm Run the Drum Clean program with 1 to 2 tablespoons of detergent
Before you touch a setting
Record this first — changing settings destroys the evidence
- Where the smell is strongest, at the tray, drum or drain
- How often Drum Clean is run
Try in this order
0 of 5 completedRun Drum Clean
ReversibleNo laundry in the drum, 1 to 2 tablespoons of detergent in main-wash chamber II.
Clean the dispenser tray
ReversibleClean the dispenser tray, by removing the tray and the insert and rinsing them under warm running water.
Wipe the housing
ReversibleWipe the housing, using hot soapy water or a mild non abrasive cleanser, and dry it with a soft towel.
Check the pump
ReversibleCheck the pump, and clean the drain pump if water is slow to leave, and then test again to see whether it helped.
Use less detergent
ReversibleUse less detergent, and use only HE detergent in the right amount, and then test again to see whether it helped.
Model-specific
What is true of this model and not of its siblings
- Hygiene routine
- Bosch's cleaning section covers the housing and control panel, the drum, descaling, the detergent dispenser tray, the water inlet strainers and the drain pump. Do not use a pressure washer, and remove residue immediately from the housing. Check the drum for metallic debris after each load, because it can rust and leave marks that look like dirt.
- Quality test water
- Every Bosch washer is tested at the factory, so a small amount of residual water may remain in the drum. Bosch recommends the Drum Clean program before the first load to remove it. A new washer that smells a little stale is therefore not necessarily faulty; the same program is the answer for a used washer that has stood unused.
- Parts for this problem on the WAT28400 (RepairClinic, 2026-09-20)
- door boot seal, part number 20007273, at $90.56; filter-fluff, part number 00647920, at $33.75; dispenser, part number 11051387, at $177.22; drain pump, part number 00145753, at $155.35.
- Other models this page answers
- These steps also fit the 300 Series WGA12400UC washer, 800 Series WAW285H2UC washer, 800 Series WGB24600UC washer.
Stop boundary
When this stops being a self-service repair
- !If the smell is burning or electrical, unplug the washer and call service
- !If sewer smell comes from the drain, check the drain connection
Evidence ledger
Sources behind this answer
Bosch's own US owner-support pages for washer error codes and self-help.
Parts and list prices as shown on RepairClinic's parts search for this model number on 2026-09-20.
Exact questions
Common questions
What is the Drum Clean program?+
A program to clean the drum and system, run with no laundry and 1 to 2 tablespoons of detergent.
How do I remove white spots in the drum?+
A small amount of descaling agent per its instructions; Bosch says descaling is normally not necessary.
Can I use steel wool on rust spots?+
No; use a chlorine-free cleansing agent.
How do I clean the housing?+
Hot soapy water or a mild non-abrasive cleanser, dried with a soft towel.
Why does the washer smell after the first use?+
It may be residual test water; run Drum Clean.
Does detergent dose affect odor?+
Yes, the detergent dose affects odor, since too much leaves residue.