First off Nixy -don't bother getting a plumber to fix an oil boiler! Most gas fitters have rarely serviced one, let alone a plumber.
I ended up fixing ours single handedly, including new fuel pump, fan, and control relay. If some oil has been spilled underneath, it will pong for ages afterwards, so first thing you need to do is make sure as much as possible is mopped up. Get rags and newspaper in all the nooks and crannies, and underneath too. Better get the flashlight out and check for any new drips too!