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

DIY fix possible

Check if the batteries in your remote thermostat controller are dead and replace them if necessary.Switch the boiler off at the fused spur for 60 seconds, then turn it back on to force a signal resync.Ensure there are no large metal objects or new electronic devices placed between the boiler and the thermostat causing interference.