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Error code reference

Bosch Washer Error Code F:25

Error of Aqua Sensor (Turbidity Sensor)

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Error of Aqua Sensor (Turbidity Sensor) — calibration of operating point failed, sensor may be calcified.

First step from the service manual

Check Aqua Sensor, check wire harness.

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

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What F:25 means on a Bosch washer

The F:25 error code on a Bosch washer indicates a failure in the Aqua Sensor system, specifically that the sensor was unable to complete its calibration of the operating point during the wash cycle. The Aqua Sensor, also called a turbidity sensor, is an optical sensor that measures water clarity to determine soil levels and optimize water usage, rinse cycles, and detergent dosing. When the control module attempts to establish a baseline calibration reading at the start of a cycle and the sensor cannot return a valid signal within the expected parameters, the F:25 fault is triggered and the cycle is interrupted.

The most common cause of this error is calcium or limescale buildup on the sensor lens, which interferes with the optical measurement and prevents accurate calibration. In hard water areas, mineral deposits accumulate over time and coat the sensor's transmitter and receiver elements, distorting or blocking the light beam used to assess water turbidity. This is why the error description specifically notes that the sensor may be calcified.

Beyond sensor fouling, wiring and connection issues can also produce this fault. The wire harness connecting the Aqua Sensor to the main control board should be inspected for damaged insulation, corroded terminals, or loose connector pins. If the harness checks out and the sensor lens is clean but the fault persists, the sensor itself may have failed internally and require replacement. In some cases the main control board may be responsible, though this is a less frequent cause.

Source: manufacturer service documentation.

Common causes of F:25

  1. 01

    Calcified or fouled Aqua Sensor lens

    Wiring / connection

    Limescale and mineral buildup on the sensor's optical lens is the most frequent trigger for F:25. The deposits block or scatter the light beam used for turbidity measurement, preventing successful calibration. Inspect the sensor face for white or chalky deposits and clean with a descaling solution.

  2. 02

    Damaged or loose wire harness connection

    Wiring / connection

    A loose, corroded, or broken connector in the harness between the Aqua Sensor and the control board can interrupt the signal and cause a calibration failure. Inspect all connector pins and wiring along the harness route for visible damage or poor seating.

  3. 03

    Faulty Aqua Sensor

    Part replacement

    If the sensor lens is clean and wiring is intact but the fault continues, the sensor's internal optical components may have failed. A defective sensor cannot produce a valid calibration signal regardless of cleaning and must be replaced.

  4. 04

    Water not filling or draining correctly before calibration

    Wiring / connection

    The Aqua Sensor calibrates using water present in the drum. If the machine has a separate water inlet or drain issue causing incorrect water levels at the calibration point in the cycle, the sensor may fail to complete calibration. Check for related fault codes or abnormal fill and drain behavior.

  5. 05

    Failed main control board

    Part replacement

    In rare cases the control board may be unable to process the signal from an otherwise functional Aqua Sensor, resulting in a false F:25 fault. This is typically diagnosed only after the sensor and wiring have been confirmed good.

See the test procedure for each cause

Frequently asked questions about F:25

What does F:25 mean on a Bosch washer?
F:25 means the Aqua Sensor, which is the turbidity or water clarity sensor in your Bosch washer, failed to complete its calibration of the operating point. The machine relies on this calibration to correctly assess water soil levels and control rinsing. The error most commonly occurs because the sensor lens has become coated with limescale, though wiring faults or a failed sensor can also be responsible.
Can I fix F:25 on my Bosch washer myself?
In many cases, yes. Start by locating the Aqua Sensor, typically mounted in the sump area or lower drum assembly, and inspect it for limescale buildup on the optical lens. Cleaning the lens with a descaling or citric acid solution often resolves the fault. You should also check that all wire harness connectors to the sensor are secure and undamaged before attempting a cycle again.
Will resetting my Bosch washer clear the F:25 error?
A reset may temporarily clear the fault code, but if the underlying cause is not addressed the error will return when the machine attempts sensor calibration again during the next cycle. Cleaning the sensor or repairing the wiring is necessary for a lasting fix. Use the reset only as a way to confirm whether the repair was successful.
Is it safe to continue using my washer when F:25 is displayed?
The F:25 code typically halts or interrupts the wash cycle, so continued operation is generally not possible without clearing the fault. Even if the machine can be restarted, running it with a non-functional Aqua Sensor means the machine cannot optimize water usage or rinsing, which may result in poor wash results or excess water consumption. Address the fault before regular use.
How much does it cost to repair a Bosch washer F:25 error?
If the fix is simply cleaning a calcified sensor, the cost can be minimal, limited to a descaling product and your time. Replacing the Aqua Sensor itself typically costs somewhere in the range of 30 to 80 dollars for the part, plus labor if a technician is involved. If the main control board is at fault, repair costs can range from 150 to 350 dollars or more depending on parts and labor in your area.

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