Your boiler isn't receiving signals from its room thermostat or controller, so it may not be heating your home as precisely as it should, though it's not a safety concern.

DIY fix possible

Switch off the boiler at its on/off switch and at the fused spur, then wait 2 minutes before switching it back on.Check that your room thermostat or controller has working batteries and is switched on, and replace the batteries if needed.Look at the thermostat's wiring at its base and the wall, and make sure no wires have come loose. Do not open the boiler casing.Switch the boiler back on and check whether the code clears. If it returns, contact a Gas Safe registered engineer.