Q. Our house was built approximately six years ago. On top of the water heater is a black something with a small tank, pipe that goes into the ceiling and a hose that leads into the floor drain. What is this for? It makes a loud siren-type noise that is getting louder. What can we do? Thanks.
A. I believe you are talking about the water expansion tank mounted on the cold water inlet pipe above your water heater. There is also a pressure-temperature relief valve that is mounted on the side of the water heater tank which has a copper pipe attached that runs down the side of the water heater. When the expansion tank fails, it can cause a pressure buildup in the water heater that is relieved by the pressure temperature relief valve, which expels water down the copper tube. While the problem could be a defective valve, it is more likely the water expansion tank mounted on the cold water inlet pipe above your water heater.
This can be easily tested by tapping on it with a metal object. When the tank is good, the lower third of the tank will give a dull thud, while the upper third will give a hollow, ringing sound. If you get a dull thud all the way up, the bladder in the tank has failed and it is filled with water. This tank will need to be replaced.
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