The thermostat displays E20, indicating a security or authentication error with Bosch cloud services.

Safety: No electrical work is required.

• Verify account: Open the Bosch app and confirm you are logged into the correct account. Log out and log back in if necessary.
• Re-link device: In the app, remove the thermostat (if visible), then follow the add-device procedure to re-register it to your account.
• Check time and date: Ensure the thermostat’s time and date are correct (either via internet sync or manual setting), as significant discrepancies can cause authentication failures.
• Update app and firmware: Install the latest version of the Bosch app and ensure the thermostat firmware is up to date.
• Wait and retry: If the issue coincides with known Bosch service maintenance, wait 30–60 minutes and try again.