Your boiler's internal clock and timer settings have lost power because the backup battery inside the control panel has failed.

What causes this fault?

This fault occurs when the small backup battery soldered onto the boiler's internal control board finally runs out of charge. Much like a CMOS battery in an old computer, its job is to save your heating schedule during a power cut, but over many years of use, it eventually loses the ability to hold power. When this happens, the boiler can no longer remember your timer settings if the mains power is switched off or interrupted.