Your boiler is currently running in a special engineer-only testing mode used to check flue gases, meaning it is not in its normal operating state.

DIY fix possible

Locate the selector switch or 'Reset' button on the control panel.Turn the selector switch back to the 'Standby' or 'Winter/Summer' position.If the code persists, restart the boiler by switching the main power off and back on after 30 seconds.