Microwave display shows E04 and unit will not start; sometimes appears after a power surge or outage.

Safety first: Disconnect the microwave from mains power before touching any internal parts.

• Power reset: Unplug the microwave for at least 10–15 minutes to allow the control electronics to fully discharge. Plug back in and check if E04 clears.
• Check power quality: Ensure the microwave is connected directly to a properly grounded wall outlet, not a multi-way adapter or surge-prone circuit. Avoid sharing the circuit with heavy appliances.
• Inspect control panel connections (if accessible from front): On some Hansa built-in models, the control panel can be removed from the front after taking out a few screws. With power disconnected, gently reseat the ribbon cable between the keypad/display and the main PCB.
• Check for moisture: If E04 appeared after steam cooking or cleaning, allow the unit to dry for several hours with the door open, then retry.
• Persistent E04: If the error remains, the main control board (PCB) or its memory (EEPROM) is likely damaged and must be replaced with the correct Hansa part number. This should be done by a qualified technician to ensure correct wiring and safety checks.

Warning: Do not attempt to reprogram or modify the control board firmware yourself; incorrect firmware can cause unsafe operation.