E20 error and thermostat shows lock icon; settings cannot be changed.

Safety first: No internal electrical work is required.

• Step 1 – Check for lock symbol: If a padlock icon is displayed, the keypad or installer lock is active.
• Step 2 – Unlock via sequence: Follow the Atlantic manual for the specific unlock sequence (often pressing and holding two keys simultaneously for several seconds).
• Step 3 – Installer code: If an installer lock code was set, enter it via the menu. If the code is unknown, a factory reset may be required (note this erases settings).
• Step 4 – Touch panel check: If certain keys appear permanently pressed (ghost touches), clean the glass/plastic surface with a soft, dry cloth. If the issue persists, the touch panel may be defective and require replacement.