Your boiler is currently stuck in a professional test mode used by engineers to check emissions, often caused by a button being held too long or a recessed switch becoming stuck.

DIY fix possible

Locate the chimney sweep button (indicated by a small radiator/bin icon) on the control panel.Press and hold the button for at least 5 seconds until the display returns to normal temperature readings.If the code persists, try turning the boiler off at the main power switch for 30 seconds and then back on.