1. Worn Carbon Brushes (Most Common)

Carbon brushes are small components that make contact with the spinning motor. They wear down naturally over time – usually after 7-10 years of regular use. When they get too short, the motor can’t get the electrical contact it needs to run properly.

This is by far the most common cause of the Bosch F43 error code. The brushes are a consumable part designed to wear out gradually, protecting the more expensive motor. Once worn below about 1cm in length, they need replacing to restore proper motor function.

2. Motor Failure (Rare)

Complete motor failure – due to bearing seizure, winding damage, or overheating – is much less common than brush wear. In most F43/E21 cases, it’s the brushes that need replacing, not the motor itself.

3. Control Module or Wiring Fault

Sometimes the issue isn’t the motor itself but the control board that drives it, or damaged wiring between the motor and control module. This can cause intermittent F43/E21 errors or the motor failing to respond to commands.

1. Diagnose the motor fault

We access the motor and check carbon brush wear, test motor windings for continuity, inspect wiring connections, and verify the control module is sending correct signals. This tells us exactly what’s failed.

2. Replace carbon brushes or motor

If it’s brush wear (most common), we fit new carbon brushes and get your machine running again. If the motor itself has failed, we replace the complete motor assembly.

3. Brief test run

After the repair, we run a brief test to make sure the drum rotates smoothly at all speeds, the motor runs quietly without vibration, and the F43/E21 error doesn’t return.

Repair or replace? Carbon brush replacement is almost always worthwhile – it’s a relatively inexpensive fix that extends the machine’s life by several more years. Motor replacement costs more, so we’ll advise honestly on whether repair makes sense based on the machine’s age and condition. Read our repair vs replace guide for more details.