This thread should be moved to "Recipes & Ingredients" rather than sit here in "Retail Shop".
If you're interested in adding some vanilla to your stout, don't boil the vanilla, do one of 2 things:
1. Soak in some vodka for the entire fermentation time then add the vodka with your priming sugar to your bottling vessel, or
2. Add to your fermenter after a week and leave for a further few weeks as if it were secondary.