What Happens in the Heater

The dip tube is an extension of the cold-water inlet to the water heater tank, extending nearly to the bottom of the tank.  Figure 1 shows a normal dip tube as it extends from the copper cold-water inlet pipe down into the tank.  The dip tube directs cold water to the bottom of the heater to be heated, allowing hot water to rise to the top of the tank.  by directing cold water to the bottom of the tank, the incoming cold water pushes the heated water out in front of it.  This allows the hot water to be used without diluting the temperature of the hot water that occupies three-fourths of the tank.

Figure 2 shows that heat has softened the plastic dip tube, and turbulence created inside the water heater has caused the dip tube to break off.  With the dip tube broken away the cold water comes into the top of the tank, creating more turbulence while reducing temperatures and requiring the thermostat to be adjusted upward.  The hot water continues to change the structure of the nonmetallic dip tube, causing it to become brittle.

Figure 3 shows that over time, the dip tube continues to change.  Cracks and fractures form all over the dip tube surface.  The turbulence  created inside the tank breaks the tube into increasingly smaller pieces. The pieces are eventually flushed out of the tank through the hot water outlet.  The missing dip tube also reduces the supply of hot water.