Bosch washer — Error Code F21

What it means

The F21 error on a Bosch front-loader signals a serious motor drive malfunction. The main control board relies on a feedback signal from the motor's tachometer to confirm rotation; if it detects irregular movement, no movement, or a complete communication breakdown with the motor control unit (MCU), it halts the cycle to prevent further electrical damage. This error acts as a hard lockout, requiring both a hardware fix and a specific manual reset. While the issue often stems from worn carbon brushes losing their connection to the commutator, it can also be triggered by a faulty tachometer, damaged wiring, or an MCU that is failing to output the necessary phase voltage.

Likely Causes

1. 1
   Worn Carbon Brushes

   This is the most common culprit in older Bosch units. When the brushes wear down past their operational limit, they lose electrical contact with the motor armature, which stops the motor from turning.
2. 2
   Faulty Motor Control Unit (MCU)

   The board tasked with powering the motor may have damaged triacs, blown capacitors, or burnt relays, causing it to fail in sending the required voltage to the motor.
3. 3
   Tachometer Failure

   The hall sensor located on the rear of the motor, which tracks RPMs, can fail. This leaves the control board blind, making it believe the motor is stationary even when it is receiving power.
4. 4
   Wiring Harness Damage

   Vibrations from heavy spin cycles can cause the wiring harness connecting the main control board, MCU, and drive motor to chafe or come loose.
5. 5
   Seized Drum or Motor Bearings

   If there is a physical obstruction between the tubs or the bearings have seized, the motor cannot turn. This creates an overcurrent condition that triggers the F21 code.

How to clear / reset

Because F21 is a hard-lock code, simply unplugging the machine won't resolve it. You must address the hardware fault first, then perform this manual reset: 1) Set the cycle dial to 'Off'. 2) Move the dial to the 8 o'clock position (typically 'Spin' or 'Empty'). 3) Wait until the F21 code appears on the display. 4) Press and hold the 'Spin Speed' button. 5) While still holding that button, turn the dial to the 9 o'clock position (typically 'Drain'). 6) Let go of the 'Spin Speed' button. 7) Turn the dial back to 'Off'. The code should now be cleared.

Common replacement parts

FAQs