Bosch's manual treats foam as a defined condition on the WAT28400UC. The foam symbol at the end of a cycle means the washer detected too much foam and automatically added a rinse; the fix is to use less detergent the next time with the same load and only HE detergent. If foam comes out of the detergent dispenser drawer the pump could not pump out the increased suds; the immediate fix is to mix 1 tablespoon of fabric softener with 1/2 liter (1 pint) of water and pour it into the detergent compartment, not with waterproof fabrics. Foam also causes E:18, repeated spinning with the Wash indicator flashing, and no spin with a wet load.
Differential
Likely causes of “Bosch 300 Series WAT28400 front-load washer shows excessive suds, SUD or Sd behavior”, and how to tell them apart
- 1
Too much detergent
What separates it The foam symbol at the end of the cycle
How to confirm Use less detergent next time with the same load
- 2
Non-HE detergent
What separates it There are heavy suds because non HE detergent was used
How to confirm Use only HE detergent, and measure it for the load
- 3
Damp or lumpy dry detergent or excess liquid
What separates it There is residue and there are suds because of damp or lumpy dry detergent or excess liquid
How to confirm Use the dosing cup for liquid detergent, and do not overfill it
- 4
A pump unable to remove suds
What separates it There is foam from the dispenser drawer because the pump is unable to remove the suds
How to confirm Use the softener mixture as an immediate fix
Before you touch a setting
Record this first — changing settings destroys the evidence
- Whether the foam symbol showed on the display
- The detergent type and the amount that you used
- Whether foam came from the drawer
Try in this order
0 of 5 completedUse less detergent
ReversibleUse less detergent, for future loads with the same wash load, and measure it, and then test again to see whether it helped.
Use HE detergent only
ReversibleUse HE detergent only, since non HE detergent is a listed cause of suds, and then test again to see whether it helped.
Apply the immediate fix if needed
Reversible1 tablespoon of fabric softener in 1/2 liter of water into the detergent compartment, not with waterproof fabrics.
Run a rinse
ReversibleRun a rinse, by using a rinse program, to remove the residue, and then test again to see whether it helped.
Clean the pump if E:18 shows
ReversibleClean the pump if E:18 shows, by following the pump maintenance steps, and then test again to see whether it helped.
Model-specific
What is true of this model and not of its siblings
- Adding the right amount of HE detergent
- Bosch's manual has a section on adding the correct amount of HE detergent and says the washer is intended for HE detergents only. It advises using the dosing cup for liquid detergent and the detergent maker's directions for load size and soil, and it lists excess suds as the leading cause of an extended wash time, wet laundry and drain error E:18.
- Foam and wash time
- Bosch's table lists excess suds (the foam symbol at the end of the cycle) as the first reason the wash cycle time is increased, alongside the balancing spins of the unbalanced load detection system. A foam event is therefore both a cleanliness problem and a time problem, and cutting the dose fixes both.
- Parts for this problem on the WAT28400 (RepairClinic, 2026-09-20)
- dispenser, part number 11051387, at $177.22; pressure sensor, part number 10009438, at $43.31.
- 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 foam overflows repeatedly with a small HE dose, call Bosch customer service
- !If E:18 shows, clean the pump, hose and drain
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 immediate fix for foam from the drawer?+
1 tablespoon of fabric softener in 1/2 liter of water poured into the detergent compartment, not with waterproof fabrics.
How do I prevent foam?+
Use less detergent and only HE detergent.
Does foam affect the spin?+
Yes; excessive suds are a listed cause of no spin and wet laundry.
Should I use the dosing cup?+
Yes, use the dosing cup for liquid detergent, to measure the right amount.