Central Heating Pumps A L Plumbing and Heating
The electronic timer or programmer is fundamentally a timed switch (right). You can set periods when the heating can be ON (subject to the other controls) and times when the heating will be OFF. Some switches have separate controls (left) for hot water and heating. Timers usually integrate an 'override' - flick a switch and the heating and/or hot water will be on continuously.
A seven day timer is recommended (left). This makes it possible to have different settings for Saturday and Sunday, and even different days of the week if required.
Note that even if the timer is ON or the heating switch is set to CONSTANT the heating system will not work if the the room or radiator thermostats are turned down.