Pry down on the valve using a screwdriver or pry bar. Check a couple of working ones so you get a feel for how much it takes to move the valve. Sticking valves should also be lower then the rest of them, site down the line and look for one shorter then the others. While you are there, look all around the valve spring, you are looking for a broken coil, that usually won't break pushrods, but it never hurts to really look it over.
Joe
