What is the purpose of the hole near the top end of a dip tube in a domestic water heater?

• A. Siphon breaker
• B. Vent passage
• C. Air vent
• D. Temperature sensor

Answer: (A)

The hole near the top of the dip tube is there to break siphons. As cold water travels down the dip tube to the bottom of the tank, pressure changes or a drop in the cold-water supply can create a suction effect that would pull water from the tank back into the cold supply line. That small hole lets air into the dip tube, interrupting the siphon and preventing the tank water (which could be hot) from being drawn back into the cold line. In short, it acts as an anti-siphon feature to prevent backflow. The other options describe devices or functions not located in that spot or not serving this purpose.