The mechanical timers you find on most boilers are quite straightforward once you get used to them, but can be confusing for a first-time user.
Start by setting it to the right time. The hands on the clock in the middle are much less important than the numbers round the outside, which correspond to the hours on a 24 hour clock. You need to turn the dial so the little black arrow is pointing to the right time, so if it’s 7.30pm (1930 in 24 hour time), the arrow should be halfway between 19 and 20.
Now your boiler knows what time it is, you can tell it when to turn on and off. That’s where the little switches come in. You’ll notice that each switch lines up with each little segment on the 24 hour clock. Push the switches in for the times you want the heating on, and out for when you want it off. Be careful not to accidentally twist the dial and change the time when you’re adjusting the switches!
Remember that it it takes about half an hour for the house to warm up after the boiler kicks in (and even longer to cool down after it’s switched off). So if you get up at 7am and leave the house at 8.30, you’ll want the boiler to switch on at 6.30 and off again at 8.