Oh, it seems a tricky question. You will get to know when you need to replace your existing toilet with the new one. The primary reason could be when you want to give your washroom a new and different look. Other reasons could be when Toilet parts will start disturbing you and will ask you costly maintenance. The flushing system starts making noise and stops conserving water. The floor drain will demand proper cleaning, and many other factors will lead you to get a new toilet for your washroom.