Well first you must work out either the make & model of your boiler -or- if it's an external timer/programmer, the make and model of that. And post another question...
They often have separate on/off for CH and DHW and some have a selector to call for permanently off / permanently on / on once a day or on twice a day. Others have separate settings for weekdays and weekends. Many have a little battery that remembers the time of day so it can start up without resetting when mains power is restored after being off.
Peccavi, February 2010
