Timer will turn the boiler on and off at certain times of day which is
useful if you want the house to be warm when you wake up and will save
you money by turning the heating off when you are out. Some boilers such
as the Baxi Platinum range have a built-in timer so they only require
a thermostat for full heating control
A Programmable Thermostat combines a timer and a thermostat to give the best control of your heating. Modern units allow you to set a temperature for several times of day so you can ask for a warm setting first thing in the morning, a low temperature for when you are out at work, a higher setting for when you return home and finally a lower temperature at night-time. Different settings can also be made for weekends and weekdays giving even more flexibility.
Programmers can be wired or radio-controlled with the radio-controlled units being much quicker to install so there is not usually much price difference between the two types.