Vaillant smart thermostat cannot be added to the Vaillant app; pairing or registration fails repeatedly.

Safety: No electrical work required.

• 1. Verify model and region: Ensure your thermostat model is supported by the Vaillant app in your country.
• 2. Use correct code: Scan the QR code on the device or enter the serial number exactly as printed, including any leading zeros.
• 3. Check for prior registration: If the device was used before, it may still be linked to another account. Ask the previous owner to remove it, or contact Vaillant support to release it.
• 4. Try again later: If Vaillant servers are busy or under maintenance, pairing may fail temporarily. Try again after some time.
• 5. Reset device: Perform a factory reset on the thermostat or gateway and repeat the onboarding process from the beginning.