Electronic timers allow you to set ‘on and off’ time periods. Some models switch the central heating and domestic hot water on and off at the same time; while others allow the domestic hot water and heating to come on and go off at different times. Electronic programmers offer a range of advanced features coupled with simplified ‘menu driven’ programming to help save energy. They come with an automatic clock and provide up to three ‘on and off’ settings for each day of the week. They supports adjusting heating programs temporarily using, ‘override’, ‘advance’ or ‘boost’.