I had a bag open up on me in some boiling water....now I double seal the bags on both ends and just put the bag in cold water and then on the heat.
It all heats up the same.....the temp of the contents of the bag is just a little less than the water...so if it gets to a slow boil, it's ready.
Here's another free tip....if you gonna potatoes that are different sizes,
if you start em in cold water they will all come up to temp at the same time...meaning they all ready at the same time.
Your welcome.