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Error code reference

Bosch Refrigerator Error Code F21

Compartment sensor in the cool-fresh compartment is interrupted (open circuit).

Bosch codesBosch refrigerator codes

Compartment sensor in the cool-fresh compartment is interrupted (open circuit).

First step from the service manual

Check the sensor and the supply cable to the electronics module.

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

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What F21 means on a Bosch refrigerator

The F21 error code on a Bosch refrigerator indicates an open circuit condition in the temperature sensor located within the cool-fresh compartment. This sensor is a negative temperature coefficient (NTC) thermistor that continuously monitors the temperature inside the cool-fresh zone and sends resistance-based readings to the main electronics module. An open circuit means the signal path is completely broken, so the module receives no valid data from that sensor.

The most common causes of this fault are a physically broken sensor element, a severed or disconnected wiring harness between the sensor and the electronics module, or a corroded connector that has lost continuity. The sensor itself can fail internally, presenting infinite resistance across its terminals. The supply cable routing through the cabinet wall or door hinge area is also a common point of failure due to repeated mechanical stress over time.

Diagnosis begins with a visual inspection of the sensor body and the full length of the wiring harness running to the electronics module. A multimeter check across the sensor terminals will confirm whether the thermistor has failed open. If the sensor reads correctly in isolation, trace the harness to its connector at the electronics module and check for continuity through each wire. A lack of continuity in any segment of the cable confirms a broken wire or damaged connector that must be repaired or replaced before the error will clear.

Source: manufacturer service documentation.

Common causes of F21

  1. 01

    Failed NTC thermistor sensor

    Part replacement

    The thermistor inside the cool-fresh compartment can fail internally, resulting in an open circuit and infinite resistance. Testing across the sensor terminals with a multimeter will confirm this if no resistance value is readable.

  2. 02

    Broken or severed wiring harness

    Part replacement

    The cable running from the sensor to the electronics module can develop breaks due to mechanical stress, especially near door hinges or cable routing clips. A continuity test along each wire in the harness will locate the break.

  3. 03

    Disconnected or loose connector

    Wiring / connection

    The sensor connector at the electronics module or at an inline junction may have worked itself loose over time. Visually inspect all connectors in the sensor circuit and firmly reseat any that show signs of looseness or partial disconnection.

  4. 04

    Corroded connector terminals

    Wiring / connection

    Moisture exposure inside the refrigerator compartment can cause the sensor or module connector terminals to corrode, increasing resistance to the point of an open circuit. Inspect terminals for oxidation or green discoloration and clean or replace the connector as needed.

  5. 05

    Faulty electronics module

    Part replacement

    If the sensor and the entire wiring harness test within normal parameters but the F21 code persists, the input circuit on the main electronics module itself may be defective. This is the least common cause and should only be considered after all other components have been ruled out.

See the test procedure for each cause

Frequently asked questions about F21

What does F21 mean on a Bosch refrigerator?
F21 indicates that the temperature sensor in the cool-fresh compartment has an open circuit, meaning the signal between the sensor and the electronics module has been completely interrupted. The refrigerator cannot read the temperature in that compartment and will display this code until the fault is corrected. The issue typically points to a failed sensor, a broken wire, or a disconnected connector in the sensor circuit.
Can I fix the F21 error on my Bosch refrigerator myself?
Checking for a disconnected or loose connector is a straightforward task that many homeowners can perform safely with the refrigerator unplugged. Testing the sensor and wiring harness for continuity requires a basic multimeter and some comfort with electrical diagnostics. Replacing the sensor or harness is also manageable for experienced DIYers, but if the fault traces back to the electronics module, professional service is recommended.
Is my food safe when the F21 code is displayed?
The cool-fresh compartment temperature may become unreliable when the F21 error is active because the control system cannot receive sensor feedback for that zone. Standard refrigerator and freezer compartments may continue operating normally if their sensors are unaffected. It is best to resolve the fault promptly and monitor compartment temperatures with a standalone thermometer in the meantime.
Will resetting my Bosch refrigerator clear the F21 error?
A power reset by unplugging the unit for a few minutes may temporarily clear the displayed code, but the error will return if the underlying open circuit condition still exists. The F21 fault is hardware-based and requires the sensor, wiring, or connector issue to be physically corrected before the code will stay clear. A reset is useful for confirming whether the fault is intermittent, but it is not a repair.
How much does it cost to repair a Bosch refrigerator F21 error?
If only the sensor needs replacement, parts and labor typically range from around 75 to 200 dollars depending on the service provider and part pricing. Wiring harness repairs can vary widely based on how accessible the damaged section is. If the electronics module is at fault, costs can rise significantly, often falling in the range of 200 to 500 dollars or more for parts and professional installation.

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