Bosch Washer Error Code F:42

The Bosch F:42 error code indicates an uncontrolled run-up of the drum motor, meaning the motor accelerated without proper regulation from the control board. In a properly functioning system, the main control board governs motor speed through a Triac, which is a bidirectional semiconductor switching component. The Triac modulates the power delivered to the motor to achieve controlled, gradual acceleration. When this Triac fails, typically due to a short circuit or thermal breakdown within the component, the motor can receive unregulated power and spin up in an unpredictable or uncontrolled manner. Bosch classifies this as a remanent error, meaning the fault is stored in the control board's memory even after power is removed.

The Triac responsible for motor control is integrated into or mounted on the main control board. A broken Triac in this context usually means it has failed in a shorted state, allowing current to pass through without proper switching control. This condition is dangerous to the motor and to the mechanical components of the washer, as uncontrolled acceleration can cause excessive drum speeds. The control board monitors motor behavior, and when it detects a run-up event outside of expected parameters, it logs the F:42 fault and halts operation to prevent further damage.

Diagnosis begins by entering the washer's test mode to reset the stored error and observe whether the fault returns during a controlled test cycle. If the fault reappears, the control board should be inspected for visible signs of Triac damage such as burn marks, cracking, or discoloration on the board surface near the motor control circuit. Because the Triac is typically soldered directly onto the control board, replacement of the entire control board assembly is the standard repair approach rather than attempting component-level soldering.