The vSMART gateway or boiler interface reports that the room thermostat unit is not detected or not paired.

Safety: This is a low‑voltage/wireless issue. No need to open the boiler.

Steps to restore detection:

• Check power/batteries: If your vSMART room unit uses batteries, replace them with fresh, high‑quality alkaline cells, observing polarity. If it is mains powered, ensure the power supply is on and the display is lit.
• Move closer to gateway: Temporarily bring the room unit closer to the vSMART internet gateway or receiver to rule out range issues.
• Reduce interference: Keep the thermostat and gateway away from large metal objects, thick concrete walls, and other 2.4 GHz devices (Wi‑Fi routers, baby monitors, cordless phones) where possible.
• Re‑pair the devices: Use the Vaillant app or thermostat menu to start the pairing process. Follow on‑screen instructions until the room unit is detected and confirmed.
• Reboot system: Restart the gateway and app after pairing to ensure stable communication.

If the room unit will not power on with new batteries or cannot be detected even at close range, the internal radio or main PCB may be faulty and the thermostat should be replaced by a qualified technician.