Oil Heating & Coal Fire?

Can any one help me as I am really mixed up with my system. I have a Rhino oil Boiler and also a coal fire. When we lit the coal fire it is meant to kick in and heat the radiators and water instead of the oil. How do I do this? I have been told to just turn the programmer on. Can I just put on the heating with out the water? Why do I need the programmer on? Why is the oil boiler firing up when I try this?