Your boiler's controller has lost track of its heating timetable, so it may not be switching on and off at the times you set, but it is not a safety problem.

DIY fix possible

Check that the date and time on the boiler controller display are correct, and correct them if not.Check that your heating and hot water timer programmes are set as you want them, and re-enter any that look wrong.Switch the boiler off at its on/off switch or the mains supply for about 30 seconds, then switch it back on.If the code clears and does not return over the next day, no further action is needed. If it comes back, contact a Gas Safe registered engineer.