Question: Water keeps dripping down the copper tube on the side of our water heater onto the floor. Is this a problem, or is it normal?
Answer: This tube is an overflow tube that will let water flow out of the tank should the pressure get too high. This tube is attached to the pressure-temperature relief valve and runs down the side of the water heater to a few inches above the floor. 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. All water heaters can suffer the effects of thermal expansion. In every tank-type water heater, cold water is heated as it enters the water heater tank. This increases the overall water volume and pressure inside the tank. For safety, the increase in volume and pressure must be relieved in some way. The way that is done in Illinois is to install an expansion tank. When an expansion tank is installed in a closed system and the temperature and pressure increases, the diaphragm inside flexes against an air cushion (air is compressible). The excess volume and pressure created by thermal expansion enters the pre-pressurized expansion tank. Installing a properly-sized and charged thermal expansion tank in a water heating system is the recommended way to eliminate the problems associated with increased volume and pressure in a closed or restricted plumbing system.
It does this with a rubber diaphragm or bladder across the middle of the tank that can absorb these pressure cycles. The failure mode for an expansion tank is for the diaphragm to rupture allowing water to displace the air in the upper half of the tank. The tank can be easily tested by tapping on it with a metal object. The lower one third of the tank will give a dull thud while the upper third of a working tank 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.
These tanks generally last 7-10 years. When you replace your water heater you should replace the expansion tank if it is older than five years.
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