Candy Recipes: I just learned how to calibrate my candy thermometer. Check the temp in a pot of boiling water. Adjust what your thermometer says compared to this chart. >>> Sea Level: Water boils at 212°F and simmers at 190°F. Slow boil - 205°F. There is more movement and noticeably larger bubbles. Real boil - 212°F. The water is rolling, vigorously bubbling, and steaming.