Vaillant vSMART app shows thermostat offline and cannot control heating or hot water remotely.

Safety first: This is a low‑voltage control issue. You normally do not need to open the boiler. Do not remove boiler covers unless you are a qualified technician.

Steps to restore connectivity:

• Check home internet: Verify other devices (phone, laptop) can browse the internet on the same Wi‑Fi network. If not, reboot the router and wait 5–10 minutes.
• Check vSMART internet gateway power: Ensure the gateway (small Vaillant box connected to router) is plugged in, its power LED is on, and the Ethernet cable is firmly connected to the router LAN port.
• Reboot the gateway: Unplug the gateway for 30 seconds, plug it back in, and wait 3–5 minutes. Check LEDs for normal status (steady power, active network light).
• Verify Wi‑Fi/router changes: If you recently changed SSID, Wi‑Fi password, or router, re‑run the vSMART setup in the Vaillant app and connect the gateway to the new network/router.
• Check Vaillant service status: If everything local is fine, check Vaillant support pages or forums for any reported cloud/server outages.
• Factory reset (last resort): If the gateway remains offline, perform a reset according to the vSMART manual and re‑pair it with the app and thermostat. Note that you may lose schedules and settings.

If the gateway LEDs do not light at all, or the device overheats or smells burnt, disconnect it and contact Vaillant or a qualified technician for replacement.