Bosch · Washing Machine
Bosch Washing Machine E21 Error Code
Motor speed sensor signal missing
What this error means
E21 indicates the motor tachometer never saw the expected RPM after the inverter applied drive—distinct from E02 where the motor is commanded but blocked. The drum may not move at all, or may jerk once then stop with E21.
How E21 is detected
When E21 appears on a Bosch washing machine, the control board has confirmed that water did not leave the machine within the programmed drain window. On Bosch WAW285H1UC, Bosch WAT28400UC, and similar variants, the drain pump runs for a fixed interval—often three to seven minutes on washers and dishwashers—while a pressure switch or turbidity sensor verifies the tub or sump is empty. If water remains, the cycle stops to prevent spin with a full tub or overflow on the next fill.
Most E21 calls are resolved without parts: unplug two minutes and verify the drum turns freely by hand. Restricted drain paths mimic pump failure because the impeller spins against a blocked hose or filter. Document whether the pump hums audibly during the drain step; a humming pump with no water movement points to a clogged filter or kinked hose, while silence may indicate a failed pump motor or loose wiring at the harness.
After clearing blockages, run a short cycle and listen at the drain hose for steady water flow. If E21 returns on the next load with a clean filter and straight hose, measure resistance at the pump motor connector per the service manual for your model before ordering a replacement pump assembly.
Common causes
- Tachometer magnet detached from the motor rotor
- Hall sensor wire broken at the stator harness
- Motor module not reading pulses due to CAN fault
- Mechanical jam preventing any drum movement
Step-by-step fixes
- 1Unplug two minutes and verify the drum turns freely by hand
- 2Run a spin-only cycle with an empty drum after reset
- 3Listen for a single rotation attempt before E21—no movement suggests sensor or module fault
- 4Avoid heavy loads until a bare-drum spin test passes
When to call a technician
Empty-drum spin failing with E21 after reset typically requires motor module or tachometer harness replacement.
Affected models
- Bosch WAW285H1UC
- Bosch WAT28400UC
- Bosch WGA12400UC
Prevention & maintenance
- Clean drain filters and hose terminations monthly on high-use washing machines to prevent E21 from lint and food debris buildup.
- Record when E21 appears in the cycle and whether it clears after a 60-second power reset on your Bosch washing machine—that detail speeds diagnosis if you call service.
- Keep the model and serial number from the rating plate when ordering parts for E21; Bosch uses multiple revisions with different harness lengths and board firmware.
- Photograph wiring connector orientation before disconnecting any component while troubleshooting E21; reversed plugs on pumps and valves cause immediate repeat faults.