It depends on the size of the sausage, how cold and the water are when you start, and whether you've sauteed it beforehand or plan to saute it afterwards. but if you want a very vague rule of thumb, I'll suggest 8to 10 minutes.
Does your recipe call for boiling the sausage? Just curious. I have steamed sausage in a saute pan with a little water and then finished them browning in some oil. I steam them for about 20 minutes. Although I have never boiled sausage I would venture a guess that 30 minutes at a rolling boil would cook them through. Maybe someone here has a more precise answer for you. Are they thick links?