Your boiler has lost its link with the wireless room thermostat, so it may not be controlling the heating from the room temperature correctly, though it can usually still provide heat.

DIY fix possible

Check the batteries in the Vitotrol room thermostat and replace them if the display is dim or blank.Make sure the thermostat display is on and shows the correct time and temperature.Switch the boiler off at its power supply or isolator switch, wait 30 seconds, then switch it back on.Check that any wall-mounted thermostat wiring you can see from outside the boiler is secure, without opening the boiler casing.If the fault code returns, contact a Gas Safe registered engineer, as the fault may be the receiver or cable.