Hansa oven shows E04 and does not start; sometimes appears after a power surge or lightning strike.

Safety first: Switch off the circuit breaker for at least 1 minute before any work.

• Power reset: Turn off the oven at the breaker for 10–15 minutes to fully discharge internal capacitors. Restore power and check if E04 clears. Sometimes this resets minor firmware glitches.
• Inspect control connections: Remove the top cover or front control panel to access the electronic control board and display/keyboard board. With power off, unplug and replug all ribbon cables and connectors to ensure good contact.
• Check for surge damage: Look for burn marks, cracked components, or a burnt smell on the control board. If present, the board must be replaced.
• Use surge protection: After repair, consider using a surge protector or dedicated line protection to prevent recurrence.

When to call a technician: E04 usually indicates a board-level fault. If a power reset and connector reseating do not resolve it, replacement or professional repair of the control module is required.