The wireless room controller has lost contact with your boiler, so the heating may not respond to its settings, though the boiler itself is usually still working.

DIY fix possible

Check the batteries in the Vitotrol room controller and replace them if they are low or flat.Switch the room controller off, wait about 30 seconds, then switch it back on and check whether the message clears.Make sure the controller is within range of the boiler and not blocked by thick walls, metal, or other interference, then check the boiler display again after a few minutes.If the fault remains, contact a Gas Safe registered engineer to check the controller's wiring, the receiver and the boiler's control connections.