Gaggenau Oven Error Code E123

E123 means the core temperature sensor (KTF) for cooking compartment 1 is reading below -10°C (50°F), which corresponds to a resistance of approximately 200 kohm. This value indicates a sensor break condition, meaning the sensor circuit is open due to a failed sensor, broken wire, or loose connection. On ovens running software version 1.20 or earlier, this code will not appear on the display even though the fault is present.

Operating the oven with a broken core temperature sensor means the appliance cannot accurately monitor compartment temperatures, which could lead to undercooked food or uncontrolled heating cycles. It is best to avoid using the oven for cooking until the sensor fault has been diagnosed and repaired. If the oven is not entering a cook cycle at all due to the error, do not attempt to bypass the fault.

If the KTF temperature sensor itself needs replacement, parts and labor costs can range from around $150 to $400 or more depending on your region and service provider. If the issue turns out to be a loose connector or damaged wire rather than a failed sensor, repair costs may be lower since no replacement part is needed. Gaggenau is a premium appliance brand, so professional diagnostic fees alone can range from $80 to $150 before any parts are ordered.

A knowledgeable DIYer can perform basic checks such as inspecting connectors and measuring sensor resistance with a multimeter. The expected resistance values are approximately 50 kohm at 25°C (77°F) and 8.77 kohm at 70°C (158°F), making it straightforward to verify whether the sensor is faulty. However, accessing the sensor wiring and running the service test programme may require disassembly and technical familiarity with the appliance, so professional service is recommended if you are not comfortable with those steps.

A power reset may temporarily clear the displayed error, but E123 will return as soon as the control board reads the sensor resistance again and detects the out-of-range value. The underlying cause, whether a broken sensor, open wire, or loose connector, must be physically corrected to permanently resolve the fault.