Bosch Microwave ER1: Convection Temperature Sensor Failing

What ER1 means

A convection recipe comes out under- or overdone, or the oven stops partway, and ER1 appears. The sensor that tells the control how hot the cavity is has begun to give unreliable readings. Without a believable temperature, convection cannot hold the set heat, so the oven either wanders or shuts the function down. Microwave-only cooking may still work normally.

Common causes of ER1

Temperature sensor failed or reading unevenly
Damaged sensor wiring or a loose connector
Control board not interpreting the signal correctly

✓ One safe check you can try

There is no safe check at home. 1. Stop using the convection function. 2. Unplug the microwave, or switch off the breaker if it is built in. 3. Write down which cooking modes still work and what the display shows. 4. Call us. Testing the sensor needs the unit de-energized and proper meters.

! Why to stop there

Sensor testing must be done with the unit fully de-energized, and the capacitor inside can hold a charge.
Reading a sensor wrong may lead you to replace the board, which costs far more than the sensor.
Convection cooking on bad readings risks scorched food or an overheated cavity.

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.

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Other Microwave codes

E1Bosch Microwave E1: Thermistor Circuit Reads Open 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 E2Bosch Microwave E2: The Safety Shutoff Stopped Your Cycle E3Bosch Microwave E3: Door Will Not Latch or Release Properly E11Bosch Microwave E11: Moisture Detected at the Control Panel E17Bosch Microwave E17: The Fast Preheat Did Not Finish

ER1ER1 questions

Can I still use the microwave function with ER1?

Often yes, since ER1 concerns convection temperature. If the unit behaves normally for plain microwave cooking, you can use that until we visit. Avoid convection until it is checked.

Will resetting the microwave fix ER1?

A reset rarely helps when a sensor is failing, because the bad reading returns as soon as it heats. It may help a loose connection briefly, but the cause usually remains.

Is a sensor replacement a big job?

Typically it is a contained repair compared with a new oven. We diagnose, give a written price before starting, and cover the work with a 30-day warranty.