Your boiler has lost contact with its room temperature sensor, so it is heating your home based only on the outdoor temperature, which usually keeps you warm but may not match the room exactly.

DIY fix possible

Turn off the power to the boiler at the fused spur or isolator switch and wait a few minutes.Check that the wires from the room thermostat or room sensor on the wall are firmly connected at both ends, and look for any visibly loose or damaged cable without opening the boiler casing.Restore the power, then reset the boiler using the reset button or the controls, and check whether the code clears.If the code returns, contact a Gas Safe registered engineer to test or replace the room sensor, as the boiler's internal wiring should not be opened by a homeowner.