Bosch washer — Error Code F21

What it means

The F21 error code on a Bosch front-load washer is a critical motor drive fault. When the main control board sends voltage to the drive motor, it expects a corresponding rotational signal back from the motor's tachometer. If the control board detects no rotation, irregular rotation, or a complete loss of communication with the motor control unit (MCU), it triggers the F21 code and aborts the cycle to prevent electrical damage. This code effectively locks out the machine until the underlying hardware issue is resolved and a manual reset sequence is performed. In most cases, the fault originates at the motor itself—specifically worn carbon brushes breaking contact with the commutator—but it can also stem from a failed tachometer, a burnt wiring harness, or a defective motor control board failing to output the correct phase voltage.

Likely Causes

1. 1
   Worn Carbon Brushes

   The most frequent cause in older Bosch washers. When brushes wear down past their limit, they lose contact with the motor armature, preventing the motor from turning.
2. 2
   Faulty Motor Control Unit (MCU)

   The board responsible for driving the motor may have burnt relays, blown capacitors, or damaged triacs, failing to send voltage to the motor.
3. 3
   Tachometer Failure

   The hall sensor on the back of the motor that monitors RPMs fails, causing the control board to think the motor is stationary even if it is receiving power.
4. 4
   Wiring Harness Damage

   Heavy spin vibrations can chafe or disconnect the wiring harness between the main control board, the MCU, and the drive motor.
5. 5
   Seized Drum or Motor Bearings

   A physical obstruction between the inner and outer tub, or seized bearings, prevents the motor from physically turning, causing an overcurrent condition that triggers the code.

How to clear / reset

The F21 error is a hard-lock code, meaning simply unplugging the washer will rarely clear it. You must fix the underlying motor issue first, then perform a manual reset. To reset: 1) Turn the cycle selector dial to the 'Off' position. 2) Turn the dial to the 8 o'clock position (usually 'Spin' or 'Empty'). 3) Wait for the F21 code to appear on the display. 4) Press and hold the 'Spin Speed' button. 5) While holding the button, turn the dial to the 9 o'clock position (usually 'Drain'). 6) Release the 'Spin Speed' button. 7) Turn the dial back to 'Off'. The code should now be cleared.

Common replacement parts

FAQs