The first thing you'll need to have checked is the updraft of your stack. Your question is very broad and it could be so many things. That water in your boiler is very dirty, and that's fine. But if you have a leak on your boiler and that water hits somewhere on the boiler that is very hot the smell that comes off would be very bad as well and could even smell like kerosense. And that's just one of many reasons. You really should have this checked out ASAP.
Sorry I couldn't be more help to you, but it's nothing to play around with, Ok..