Does the tank look similar to that one? If so then locate the input/output pipes for the coil as in the diagram and see if they are heating at all. If not and the reason is not simply the sort of valve/cock mentioned above then you may simply need to get a plumber to look at the system.wouldn't be too well up on DIY myself.
Er - the rads are working so I doubt that the boiler or oil is the problem!Is the boiler comming on ? Not being smart but have you checked your tank for oil ? also if it was low then refilled, it maybe airlocked........