Bosch Microwave Error Code Er4 — Extreme Overheating
What this means
Error Er4 is a critical safety alert indicating extreme overheating inside the microwave, potentially from a fire. This can occur when metallic objects, foil, or unsuitable containers create arcing, or when food items ignite. Do not open the door if you suspect a fire inside.
Step-by-step fix
4 stepsDo NOT open the door
If there is smoke or you suspect a fire inside, keep the door closed. Opening it would feed oxygen to any flames.
A closed microwave will suffocate a small fire.
Disconnect power
Unplug the microwave or turn off the circuit breaker immediately.
Wait for cooling
Allow the microwave to cool completely before opening the door. This may take 30 minutes or more.
Inspect for damage
Once cool, open the door and check for charred food, melted containers, or damage to the interior. Clean thoroughly.
If the interior wall paint is damaged or the waveguide cover is burned, the microwave may not be safe to use.
When to call a professional
If there is internal damage to the microwave cavity or components, do not use the microwave. Have it inspected or replaced.
Information compiled from manufacturer service manuals, official troubleshooting documentation, and appliance repair industry resources. This guide is for informational purposes only — always consult a qualified technician for complex repairs.
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