Bosch Microwave E1: Thermistor Circuit Reads Open

What E1 means

On a Bosch built-in speed microwave oven, the display flashes E1 for three seconds and the oven drops back to plug-in mode. Behind it, the control found the thermistor circuit open, as if the sensor were disconnected. That sensor tracks the temperature for the convection and combination functions, so those modes become unavailable. Plain microwave cooking is the part that still works.

Common causes of E1

Thermistor burned out and open
Broken wire or loose plug in the sensor circuit
Input module failing to read the sensor properly

✓ One safe check you can try

1. Switch the oven off at the breaker, wait two minutes, and switch it on again; this is worth one try for an intermittent contact. 2. Test it with a plain microwave cycle. 3. Do not take the cover off: the high-voltage capacitor can hold a dangerous charge even when unplugged. 4. If E1 returns, call us.

! Why to stop there

The capacitor inside stays dangerous after disconnecting, so opening the oven is not a household task.
An open sensor and a loose connector look the same without meter readings, so guessing wastes money.
Replacing the input module first can cost far more than a thermistor.

Opening a panel yourself does not automatically cancel a manufacturer warranty, but it can cause accidental damage, and some manufacturers set their own service conditions. Check your warranty terms, or ask us, before deciding.

→Same appliance

Other Microwave codes

E4Bosch Microwave E4: The Thermistor Circuit Reads Shorted E-04Bosch Microwave E-04: Over-the-Range Humidity Sensor Not Reporting E-11Bosch Microwave E-11: Over-the-Range Key Read as Held for a Minute ER1Bosch Microwave ER1: Convection Temperature Sensor Failing ER4Bosch Microwave ER4: Severe Overheating, So Stop Using It ER11Bosch Microwave ER11: A Control Key Is Jammed E2Bosch Microwave E2: The Safety Shutoff Stopped Your Cycle E3Bosch Microwave E3: Door Will Not Latch or Release Properly

E1E1 questions

Why does the oven switch to plug-in mode with E1?

With the thermistor unreadable, the oven drops the modes that depend on it and keeps basic microwave cooking available. The display shows the code briefly to tell you something is wrong.

How does E1 differ from the E4 code?

No. E1 means the thermistor circuit reads open, while E4 means it reads shorted. They look similar on the display but have different causes, and a technician checks which one applies.

How soon should E1 be fixed?

Not urgently if you only microwave. If you rely on convection, book a visit. We quote in writing before starting and our repair carries a 30-day warranty.