In a boil over, where does the boiling water occur?

• A. The bottom of the tank
• B. The top of the tank
• C. In the vent line
• D. In the overflow pipe

Answer: (A)

Boiling begins where heat is applied. In a boil over, the heater sits at the bottom of the tank, so the water there reaches its boiling point first and starts to form steam. This vigorous boiling creates foam and pushes liquid upward, eventually spilling over the top. The top of the tank isn’t where the boiling itself happens, it’s where the liquid overflows. The vent line is for releasing steam, and the overflow pipe simply carries away spilled liquid. So the boiling water occurs at the bottom of the tank.