Indoor unit will not start, display shows E0 shortly after power-on

Safety first: Turn off the breaker supplying the indoor unit and confirm power is off before removing any covers.

Steps:

• Power reset: Turn the AC OFF at the remote, then switch OFF the dedicated breaker for 5–10 minutes. Restore power and try again. Sometimes transient EEPROM errors clear after a full reset.
• Check indoor PCB connections: Remove the front panel and control box cover of the indoor unit. Inspect the main control PCB for loose connectors, especially the small harnesses going to the memory/EEPROM IC. Reseat all multi-pin connectors firmly.
• Look for surge damage: Visually inspect the PCB for burn marks, bulged capacitors, or a burnt smell. If present, the board is likely damaged and must be replaced.
• Try factory reset (if supported): Some Mitsubishi Electric models allow a reset via the remote (e.g., press and hold RESET or a combination like ON/OFF + TEMP ▼ for several seconds). Refer to the model’s service manual.
• Replace indoor PCB: If E0 persists after reset and connections are confirmed good, the indoor control PCB (with EEPROM) must be replaced. Match the part number printed on the existing board.

When to call a technician: If you are not comfortable working around electronics or the PCB shows visible damage, have a qualified Mitsubishi Electric technician replace and initialize the board.