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Error code reference

Bosch Refrigerator Error Code F40

In the descaling programme the temperature on the ice rod has not risen above 5°C for 5 minutes (appliances…

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In the descaling programme the temperature on the ice rod has not risen above 5°C for 5 minutes (appliances from KI 22 and Eprom version 6.01).

First step from the service manual

Check heater actuation and condition, safety thermal cut-out, sensor, and refrigerant solenoid valve.

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

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  • Step-by-step tests with expected resistance, voltage, and continuity values
  • Wiring diagram references and connector pinouts from the OEM service manual
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What F40 means on a Bosch refrigerator

The F40 error code on Bosch refrigerators (applicable to models from the KI 22 series with EPROM version 6.01 and later) is generated during the automatic descaling programme. Specifically, the control board monitors the temperature at the ice rod sensor during this cycle. If the temperature fails to rise above 5 degrees Celsius within a 5-minute window, the system flags F40 as a fault. This indicates the descaling heat cycle is not completing as expected, pointing to a failure in the heating circuit, temperature sensing, or refrigerant flow control.

The descaling programme relies on a heater to warm the ice rod area, melting any scale or ice buildup. When the heater fails to actuate properly, or when a safety thermal cut-out has tripped and broken the heating circuit, the ice rod temperature simply will not climb to the required threshold. A faulty sensor can also cause this fault if it is reading temperatures incorrectly, making the control board believe the threshold has not been reached even when heating is occurring normally.

The refrigerant solenoid valve is another critical component in this circuit. If the solenoid valve is stuck open or not closing correctly, refrigerant flow may continue to cool the ice rod area during the descaling cycle, counteracting the heater and preventing the temperature rise the system requires. Diagnosis should begin with checking heater actuation and continuity, inspecting the safety thermal cut-out for an open circuit, testing the ice rod temperature sensor for accurate readings, and verifying proper operation of the refrigerant solenoid valve.

Source: manufacturer service documentation.

Common causes of F40

  1. 01

    Heater failure or lack of actuation

    Part replacement

    The heater responsible for warming the ice rod during the descaling cycle may have failed or is not being activated by the control board. Check for continuity through the heater element and verify the control board is sending the correct actuation signal.

  2. 02

    Tripped or faulty safety thermal cut-out

    Part replacement

    The safety thermal cut-out is designed to open the heating circuit if temperatures exceed a safe limit. If it has tripped or failed permanently open, the heater will receive no power and the ice rod temperature will not rise.

  3. 03

    Defective ice rod temperature sensor

    Part replacement

    If the sensor monitoring the ice rod is out of calibration or has failed, it may report temperatures below 5 degrees Celsius even when the heater is functioning normally. Verify the sensor's resistance values against specification to confirm accuracy.

  4. 04

    Refrigerant solenoid valve not closing

    Part replacement

    A solenoid valve that fails to close during the descaling programme will allow refrigerant to continue circulating and cooling the ice rod area, preventing the required temperature rise. Inspect the valve for proper electrical actuation and mechanical operation.

See the test procedure for each cause

Frequently asked questions about F40

What does F40 mean on a Bosch refrigerator?
F40 indicates that during the automatic descaling programme, the temperature at the ice rod sensor did not rise above 5 degrees Celsius within the required 5-minute period. This fault applies to Bosch refrigerators in the KI 22 series and those running EPROM version 6.01 or later. It points to a problem in the heating circuit, temperature sensing, or refrigerant flow control during the descaling cycle.
Can I fix the F40 error on my Bosch refrigerator myself?
Some basic checks, such as inspecting wiring connections to the heater and sensor, can be done by a knowledgeable DIYer. However, testing the safety thermal cut-out, verifying sensor resistance values, and diagnosing the refrigerant solenoid valve typically require a multimeter and familiarity with refrigerator electrical systems. Any work involving the refrigerant circuit should be performed by a licensed technician.
Will resetting my Bosch refrigerator clear the F40 error code?
A reset may temporarily clear the F40 code, but if the underlying fault in the heater, thermal cut-out, sensor, or solenoid valve has not been repaired, the code will return the next time the descaling programme runs. Clearing the code without addressing the root cause does not resolve the problem and could allow scale buildup to continue unchecked.
Is it safe to keep using my refrigerator when F40 is displayed?
The F40 fault is specific to the descaling programme and does not necessarily mean the refrigerator will stop cooling immediately. However, a failed heater circuit or malfunctioning solenoid valve can affect ice maker performance and long-term reliability. It is advisable to have the fault diagnosed and repaired promptly rather than ignoring it.
How much does it cost to repair a Bosch refrigerator F40 error?
Repair costs depend on which component has failed. Replacing a temperature sensor or thermal cut-out is generally less expensive, typically in the range of 80 to 200 dollars including labor. A faulty heater assembly or refrigerant solenoid valve replacement can run higher, potentially 150 to 400 dollars or more, depending on parts availability and local labor rates.

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