Your boiler has detected that the water temperature has dropped too low and is automatically running to prevent the pipes from freezing.

DIY fix possible

Check that your gas supply is turned onEnsure the boiler power switch remains on so the protection can finish its cycleIf it is very cold, check that the white plastic condensate pipe leading outside isn't frozen solidOnce the boiler warms the internal water above 14°C, the code will disappear automatically