I started a brisket at 155°F before bed, planning to let it go for 24 hours. Woke up to find the circulator had shut down due to low water level. The brisket sat in lukewarm water for who knows how long. Had to throw it out.
What I Missed
Water evaporates during long cooks, especially if your container is not covered. The circulator needs a minimum water level to function. When that level drops below the sensor, it shuts down to prevent damage.
I assumed filling the container at the start line was sufficient. For a four-hour cook, maybe. For 24 hours, definitely not.
How I Handle Long Cooks Now
I cover the container with plastic wrap or foil to minimize evaporation. I also fill the water to the maximum line instead of the minimum. For cooks over 12 hours, I check the level once before bed.
I also learned that some foods are not worth the overnight risk when you are still learning. Now I do long cooks on weekends when I can monitor them, at least until the process becomes automatic.