Charger shows E22; app indicates 'Button panel error' or 'User interface fault' on models with physical buttons.

Safety first: Disconnect power before removing the front panel.

Steps:

• Inspect front panel: Check for cracks, signs of impact, or water streaks around the buttons or LEDs.
• Dry the unit: If moisture is suspected, leave the charger powered off with the cover removed in a dry environment for at least 24 hours.
• Check ribbon cable: Ensure the front panel ribbon cable is fully seated at both the panel and main board ends.
• Replace front panel: If E22 persists and the cable is intact, replace the Walli front user interface panel assembly.