For water that moves in a Bosch WAT28400UC at the wrong time, Bosch's manual is specific about the drain: if the end of the drain hose touches the discharge water it can be sucked back into the appliance and may damage the washer or textiles, so make sure there is no stopper in the sink drain, the hose end does not touch the discharge water, and the sink drain is free flowing. The hose is positioned with the supplied elbow 4 inches from its end and secured with a nylon tie strap when it goes into a standpipe. Water that cannot be seen in the drum is normal: the water level in a high-efficiency front-loader is below the visible part of the drum.
Differential
Likely causes of “Bosch 300 Series WAT28400 front-load washer fills with water while turned off”, and how to tell them apart
- 1
A drain hose end in the discharge water
What separates it Water is sucked back into the washer because the drain hose end is in the discharge water
How to confirm Keep the end clear of the water; no stopper in the sink
- 2
A partly clogged sink or drain pipe
What separates it Water backs up and returns because the sink or the drain pipe is partly clogged
How to confirm Make sure that the drain is free flowing, and clear any clog
- 3
A hose not secured with the elbow and tie strap
What separates it The hose comes out of the pipe because it is not secured with the elbow and tie strap
How to confirm Position the elbow 4 in from the end and secure it
- 4
A supply hose or valve leak
What separates it Water appears with the washer idle because of a supply hose or valve leak
How to confirm Close the taps and check the hoses and washers
Before you touch a setting
Record this first — changing settings destroys the evidence
- Where the drain hose ends and whether it touches the water
- Whether the sink drain is free flowing
- Whether water enters with the taps closed
Try in this order
0 of 5 completedClose the taps
ReversibleClose the taps, and see whether the water level stops changing, and then test again to see whether it helped.
Check the drain hose end
ReversibleCheck the drain hose end, since it must not touch the discharge water, and then test again to see whether it helped.
Check the drain
ReversibleCheck the drain, which must have no stopper and be free flowing, and then test again to see whether it helped.
Secure the hose
ReversibleElbow 4 in from the end, nylon tie strap, or a hose clip on a sink siphon.
Test with a short cycle
ReversibleTest with a short cycle, and watch the fill and the drain, and then test again to see whether it helped.
Model-specific
What is true of this model and not of its siblings
- Drain connection options
- Bosch's installation section shows three drain connections: a standpipe, where the elbow supplied is fitted 4 in from the end of the hose and secured with a nylon tie; a sink siphon, where the hose is secured with a 0.9 to 1.6 in hose clip; and a wash basin, where the hose must be attached securely and not touch the discharge water. Do not reuse an old drain hose or kink or modify the drain hose.
- Supply hoses and colors
- The water connection hoses are color coded: red is the hot water hose and blue is the cold water hose, each attached hand tight at the tap and at the back of the washer. Rubber washers must be seated at both ends and the connections checked for leaks. A hose that is twisted, kinked, pinched or caught can restrict water flow and damage the hose.
- Parts for this problem on the WAT28400 (RepairClinic, 2026-09-20)
- water inlet valve, part number 00635399, at $146.39.
- 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 water enters with the taps closed, unplug the washer and call Bosch customer service
- !If water reaches the floor, shut off the supply and call service
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
Why does water come back into my Bosch washer?+
A drain hose end that touches the discharge water can be sucked back into the appliance.
Can I see the water in the drum?+
Not always; the level in a high-efficiency front-loader is below the visible part of the drum.
How do I secure the drain hose?+
With the elbow and a nylon tie strap in a standpipe, or a 0.9 to 1.6 in hose clip on a sink siphon.
Should the sink drain have a stopper?+
No; there must be no stopper in the sink drain.
What if the water keeps coming?+
Close the taps and call service.
Is there a drain height rule?+
See the installation section; the hose must not be kinked or modified.