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Error code reference

Miele Dishwasher Error Code F42

Line frequency registration fault

Miele codesMiele dishwasher codes

Line frequency registration fault — it cannot be established whether the line frequency falls within the 50±5 Hz or 60±5 Hz range.

First step from the service manual

Have the main power supply checked by a specialist.

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

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What F42 means on a Miele dishwasher

The F42 error code on a Miele dishwasher indicates a line frequency registration fault. The dishwasher's control electronics continuously monitor the incoming AC power supply frequency to confirm it falls within one of two expected ranges: 50 Hz (plus or minus 5 Hz) or 60 Hz (plus or minus 5 Hz). When the control board cannot identify the frequency as belonging to either range, it triggers F42 and halts operation. This is a protective function designed to prevent the motor, pump, and control systems from operating under abnormal electrical conditions.

The most likely source of this fault is an issue with the external power supply rather than a failed internal component. Severe voltage fluctuations, unstable grid power, or an interrupted neutral connection can distort the AC waveform enough that the control electronics cannot accurately read the frequency. In some cases, problems with the home's breaker panel, incoming service line, or a heavily loaded circuit shared with high-draw appliances can contribute to this instability.

Because the fault originates at the power supply level, the recommended first step is to have a qualified electrician inspect the dedicated circuit and main supply feeding the dishwasher. If the supply power tests within normal parameters and the fault persists, the control board responsible for frequency detection may itself be faulty and would require professional evaluation and likely replacement.

Source: manufacturer service documentation.

Common causes of F42

  1. 01

    Unstable or fluctuating grid power supply

    Wiring / connection

    Power instability from the utility grid can cause the AC frequency to fall outside the detectable range of 45 to 65 Hz, triggering F42. This is often intermittent and may coincide with outages, brownouts, or high-demand periods on the local grid.

  2. 02

    Faulty or loose electrical connection at the circuit breaker or service panel

    Wiring / connection

    A loose neutral wire, failing breaker, or degraded connection in the home's electrical panel can distort the waveform delivered to the dishwasher. An electrician can identify this during an inspection of the supply circuit.

  3. 03

    Overloaded shared circuit

    Wiring / connection

    If the dishwasher shares a circuit with other high-draw appliances, the combined load can cause voltage and frequency disturbances that interfere with frequency registration. Verifying the dishwasher is on a properly rated dedicated circuit is part of the evaluation.

  4. 04

    Faulty control board

    Part replacement

    If external power supply checks out as normal and the error persists, the control board's internal frequency detection circuitry may have failed. This would require professional diagnosis and board replacement.

See the test procedure for each cause

Frequently asked questions about F42

What does F42 mean on a Miele dishwasher?
F42 is a line frequency registration fault, meaning the dishwasher's control electronics cannot confirm that the incoming AC power frequency falls within the expected 50 Hz or 60 Hz range (each with a plus or minus 5 Hz tolerance). The dishwasher stops operating as a protective measure. The fault points to a problem with the power supply feeding the appliance rather than a mechanical failure inside the unit.
Can I fix the F42 error myself?
The first step requires a qualified electrician or appliance specialist to inspect your home's power supply and dedicated circuit, so this is not a typical DIY repair. If the power supply is confirmed to be normal and the fault continues, a technician will need to evaluate the control board. Do not attempt to bypass or ignore this fault, as running the appliance on abnormal power can cause further damage.
Is it safe to use my dishwasher while it shows F42?
No, you should not attempt to operate the dishwasher while the F42 fault is active. The error indicates that the control system cannot confirm the power supply is within safe operating parameters. Running the appliance under these conditions risks damage to the motor, pump, and control electronics.
Will resetting the dishwasher clear the F42 error?
A simple power reset is unlikely to permanently clear F42 if the underlying power supply issue has not been resolved. The fault will typically return as soon as the control board again fails to detect a valid frequency on startup. The root cause, whether a supply problem or a faulty control board, must be addressed first.
How much does it cost to repair a Miele dishwasher showing F42?
If the issue is with the home's electrical supply or circuit, electrician fees typically range from $75 to $250 or more depending on the work required. If the control board itself needs replacement, repair costs including parts and labor generally range from $200 to $500 or higher, depending on the specific model and local labor rates.

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