When making marmalade at home, don’t try to make too big a quantity at one go. Make sure you have large enough pans. A proper, wide-rimmed, thick-bottomed jam pan is not essential, but it is great if you have one. A copper pan is not essential either, but it will retain the heat and help the whole process. If you try to make too great a quantity, it will take a long time to come to the boil and will not boil rapidly enough to achieve a good set.
I always grease the base of the marmalade pan with a thin skim of unsalted butter before adding the ingredients.