Microwave shows E12 and may continue to run the fan after cooking or refuse to start.

Safety warning: Internal sensors are located near hot surfaces and live wiring. Only perform external checks unless you are trained.

Steps to try:

• 1. Allow cooling: Allow the microwave to cool completely with the door open, then disconnect and reconnect power.
• 2. Avoid extreme use: If E12 appears after repeated long cooking cycles, reduce back-to-back usage to prevent excessive oven cavity temperatures.
• 3. Test basic heating: Try a short 30-second heating cycle with a cup of water. If E12 appears immediately, the cavity temperature sensor circuit is likely faulty.
• 4. Technician-level: Access the cavity NTC sensor (often mounted on the cavity wall or top), measure its resistance at room temperature, and compare the reading to Siemens specifications. Replace the NTC sensor or main control PCB as indicated by diagnostics.

Do not bypass temperature sensors; they are critical safety devices for preventing overheating.