Your boiler has lost its wireless connection to your room thermostat or controller, meaning it doesn't know when to turn your heating on or off.

DIY fix possible

Check the batteries in your room thermostat and replace them with fresh ones.Turn the boiler off at the fused spur for 60 seconds to reset the receiver, then turn it back on.Attempt to re-pair the thermostat to the receiver following the instructions in your user manual.