E21
Bosch Oven
Severity:What Does This Error Mean?
Bosch oven E21 means the oven cavity temperature sensor (NTC or PT1000 probe) has failed or its wiring has a fault. Inspect the sensor probe inside the oven — it is a thin metal rod mounted on the rear or side wall — for any visible damage or burn marks. If the probe looks intact, test its resistance with a multimeter before ordering a replacement.
Affected Models
- Bosch Series 2 Oven
- Bosch Series 4 Oven
- Bosch Series 6 Oven
- Bosch Series 8 Oven
- Bosch HBN Series Built-In Oven
Common Causes
- Oven temperature sensor probe burnt out or developed an open circuit after extended high-temperature use
- Wiring between the sensor probe and the control board is damaged, often by oven self-clean heat
- Sensor connector on the control board has corroded or a pin has pushed back
- Sensor shorted to ground after liquid from boiling dishes contacted the probe connection point
- Control board temperature sensing circuit has developed a fault (less common than sensor failure)
How to Fix It
-
Switch off and allow the oven to cool completely
Always disconnect the oven from the mains before inspecting any internal components. Allow at least 30 minutes for the oven to cool after use.
-
Locate and inspect the temperature sensor
The temperature sensor is a thin metal probe (typically 4–6 cm long) mounted inside the oven on the rear or upper side wall. Check for visible damage — discolouration, burn marks, or a broken probe tip indicate sensor failure.
-
Test the sensor resistance
Disconnect the sensor wiring connector (accessible from behind the oven rear panel). Bosch ovens use a PT1000 sensor — it should read approximately 1,080 Ω at 20°C. A reading of 0 or OL indicates failure.
-
Replace the temperature sensor
Order a genuine Bosch temperature sensor for your model (check the E-number on the rating plate inside the door frame). Unscrew the old sensor, disconnect the wiring, and fit the new one. Cost is typically $20–45.
-
Test the oven
Reconnect the oven to the mains and run it on a standard bake function at 180°C for 10 minutes. If E21 has cleared and the oven heats normally, the repair is complete.
When to Call a Professional
Replacing the oven temperature sensor is a straightforward repair most owners can do. If E21 returns after installing a new sensor, the control board has failed and requires Bosch-certified service.
Frequently Asked Questions
What type of sensor does a Bosch oven use for E21?
Most Bosch built-in ovens use a PT1000 platinum resistance temperature sensor. At 20°C it reads approximately 1,080 Ω. At 200°C it reads approximately 1,753 Ω. These readings confirm whether the sensor is working.
E21 appeared right after a pyrolysis self-clean cycle — why?
Pyrolysis cleaning reaches temperatures above 450°C, which is extreme stress for the sensor and its wiring. It is common for the temperature sensor or its wiring insulation to fail during or after a pyrolysis cycle.
My Bosch oven shows E21 but still heats — should I be concerned?
Yes — if the oven heats with E21 active, the sensor is giving incorrect readings and the oven cannot regulate its temperature. It may overheat or underheat without any safety cutout. Do not use it until the sensor is replaced.