What E1 Means
E1 on a Bosch built-in speed microwave oven means the thermistor circuit is reading open. The service manual notes the behaviour precisely: the appliance reverts to plug-in mode and displays the code for three seconds. The thermistor is the temperature sensor the oven relies on for its convection and combination functions, so an open circuit there takes those modes out of use.
Common Causes of E1
- Thermistor failed open
- Broken wire or loose connector in the thermistor circuit
- Input module fault reading the sensor
🔧 One Safe Check You Can Try
Switch the appliance off at the breaker for two minutes and back on, which is worth one attempt for an intermittent connection. Do not open the housing: the high-voltage capacitor inside a microwave can hold a dangerous charge even after it is unplugged.
⚠ Why You Shouldn't Go Further Than That
- The high-voltage capacitor in a microwave stores a charge that remains dangerous after the appliance is disconnected, and it must be discharged by someone trained to do it.
- The thermistor sits in the cavity airflow near the convection heating components, which is not an area to explore.
- Bosch's troubleshooting works through the input module as well as the sensor, and only one of those is a cheap part.
- Built-in speed ovens are trimmed into cabinetry, so removal without the right method damages the surrounding units.
Opening a panel to inspect or repair something yourself doesn't automatically cancel your manufacturer's warranty — but it can risk accidental damage, and some manufacturers do have specific service conditions. Check your product's warranty terms, or ask us, before deciding.