mypros+
Error code reference

Bosch Washer Error Code 42

Uncontrolled run-up of drum motor

Bosch codesBosch washer codes

Uncontrolled run-up of drum motor - control broken (Triac broken).

First step from the service manual

Reset error with activating test mode, check control.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

MyPros+ Max

Get the full diagnostic procedure for 42.

  • Step-by-step tests with expected resistance, voltage, and continuity values
  • Wiring diagram references and connector pinouts from the OEM service manual
  • Verified part numbers when replacement is required
Get the full procedure

$29/month · Cancel anytime · Or $9.95 3-day pass

What 42 means on a Bosch washer

Error code 42 on a Bosch washer indicates an uncontrolled run-up of the drum motor, which the control unit has detected as a Triac failure. The Triac is a semiconductor switching component on the main control board responsible for regulating power delivery to the drum motor. When the Triac fails in a shorted or open state, it loses the ability to properly gate motor current, resulting in the motor receiving unregulated voltage. This causes the drum to accelerate in an uncontrolled manner or behave erratically, prompting the control board to log error code 42 and halt operation.

The root cause is nearly always a failed Triac on the main control board. Triacs can fail due to power surges, excessive current draw from a worn motor, or simple age-related component degradation. A shorted Triac is the most common failure mode and will typically cause the motor to spin immediately and uncontrollably when power is applied. In some cases the surrounding circuitry on the control board may also sustain damage, so the board should be inspected carefully before ordering replacement parts.

The first diagnostic step is to reset the error by entering the washer's test mode, then evaluate the condition of the main control board. If the error returns immediately or the drum exhibits uncontrolled movement during the test cycle, the control board requires replacement. It is also worth inspecting the motor and motor wiring harness for signs of a short circuit or overload condition that may have contributed to the Triac failure in the first place.

Source: manufacturer service documentation.

Common causes of 42

  1. 01

    Failed Triac on main control board

    Part replacement

    The Triac is a semiconductor switch that controls motor power. When it fails in a shorted state, it allows unregulated current to reach the motor, causing uncontrolled drum spin. This is the most direct cause identified by this error code.

  2. 02

    Damaged main control board (broader failure)

    Part replacement

    A Triac failure can sometimes damage surrounding components on the control board. If the board shows visible burn marks, scorched traces, or swollen capacitors near the motor drive circuit, the entire board will need replacement rather than component-level repair.

  3. 03

    Power surge or voltage spike

    Part replacement

    A sudden spike in line voltage can destroy the Triac. If error code 42 appeared after a power outage, storm, or electrical event in the home, a surge is a likely contributing factor. Installing a surge protector on the washer circuit can prevent recurrence.

  4. 04

    Motor winding short circuit

    Part replacement

    A short in the drum motor windings can cause excessive current to flow through the Triac, overloading and destroying it. Inspect the motor and its wiring harness for signs of burning, melted insulation, or abnormal resistance readings before replacing the control board.

  5. 05

    Loose or damaged motor wiring harness

    Wiring / connection

    A wiring harness that has frayed insulation or poor pin connections at the control board connector can create intermittent shorts that stress the Triac. Inspect all connectors between the control board and motor for corrosion, damage, or looseness.

See the test procedure for each cause

Frequently asked questions about 42

What does 42 mean on a Bosch washer?
Error code 42 on a Bosch washer means the control board detected an uncontrolled run-up of the drum motor, and has identified the cause as a broken Triac on the main control board. The Triac is the semiconductor component responsible for switching and regulating power to the motor. When it fails, the motor can spin erratically or without command, so the washer shuts down to prevent damage or injury. This error almost always requires control board inspection or replacement.
Can I reset error code 42 on my Bosch washer myself?
Yes, you can attempt a reset by activating the washer's test mode, which is the recommended first diagnostic step. However, if the underlying Triac or control board failure is not addressed, the error will return immediately or very quickly. A reset alone will not fix the root cause, but it is a useful starting point to confirm the fault is active and repeatable.
Is it safe to use my Bosch washer when error code 42 is showing?
No, you should not continue using the washer while error code 42 is active. An uncontrolled motor run-up means the drum could spin without proper regulation, which can cause mechanical damage to internal components and creates a potential safety hazard. The washer should remain out of service until the control board has been inspected and repaired or replaced.
How much does it cost to fix error code 42 on a Bosch washer?
Repair costs depend on what component has failed. If only the control board needs replacement, parts typically range from $150 to $400 depending on the model, with labor adding $100 to $200 if a technician is hired. If the drum motor has also been damaged, total repair costs can be higher. Getting a diagnostic assessment before committing to repairs is advisable, especially on older machines.
Will replacing the control board fix error code 42 on a Bosch washer?
In most cases, yes, replacing the main control board resolves error code 42 because the failed Triac is integrated into that board. However, before installing a new board, it is important to inspect the drum motor and wiring harness for any shorts or damage that caused the original Triac failure. Replacing the board without addressing an underlying motor fault can result in the new board failing as well.

Related Bosch washer codes

All Bosch washer codes
View all 123 Bosch washer codes

78,000+ service manuals · 160,000+ error codes · 55+ brands

Get Started

$29/month · Cancel anytime · Or $9.95 3-day pass