Your boiler is running a routine self-check to fine-tune how it burns gas, and it has flagged that it is not getting enough heat away from the burner, which is often fixed by a simple reset and a quick check of the heating system.

DIY fix possible

Check the pressure gauge on the front of the boiler when the system is cold; it should read between 1.0 and 1.5 bar. If it is low, top it up using the filling loop as shown in the manual, then close the loop valves.Bleed any radiators that are cold at the top or feel cooler than the rest, using a radiator key, and check the pressure again afterwards.Press the reset button marked R on the boiler control panel and let the boiler run its calibration without interruption for a few minutes. If the code returns, stop and call a Gas Safe registered engineer.