How do you work the timer controls on a Worcester 240 Combi RSF Boiler?

Can anyone help us? We have a Worcester 240 Combi RSF Boiler in our rented house. The heating works when you turn it on, as a one off. However; when you try and set it up so it comes on automatically through the timer option it doesnt seem to work. How do we know we have set it up correctly and is there anywhere we can get full instructions (if we haven't, as the user operating instruction manual we have doesn't tell you about the timer functionality!)

We are getting cold!

Thank you!