The boiler's control panel has lost track of its heating schedule, so it may not switch on and off at the times you have set, though it can often keep running as normal.

DIY fix possible

Check the date and time shown on the boiler's control panel and correct them if they are wrong.Check that your heating and hot water timer settings are still in place, and set them again if needed.Switch the boiler off at its on/off switch, wait about 30 seconds, then switch it back on.If the code is still showing, press the reset button on the control panel as described in your user manual, then check whether the code returns after a few hours.