Troubleshooting Your Thermal Expansion Tank

A crucial aspect of plumbing, troubleshooting your thermal expansion tank may be necessary at times, especially if you cannot get a plumber in time. Generally speaking, heat creates a pressure increase, or an expansion, which can affect the volume of water. Also, the higher the pressure, the higher the temperature, so keeping the pressure down is a must simply for safety’s sake. Troubleshooting itself is just a fancy term of fixing something by locating the problem area. Just as in any DIY project, you will need to do some research, not online, but by scavenging any symptoms—noises, temperature variations, etc.—so that you can diagnose and solve, as a true doctor of plumbing.


Without a thermal expansion tank, heat from the water heater will cause an increase in pressure as it expands, and the new volumes of water can create havoc throughout your plumbing, which could lead to water damage, mold, scalding steam, and other unsafe conditions. Moreover, if an expansion tank is absent, the first sign that something is wrong is leaking; too much water with excess heat and pressure in a pipe will cause leakage. However, if you do have a thermal expansion tank, and leakage persists, it may mean that the leaking pipes are within a closed water system. In other words, for some reason the tank is not doing its job in a certain area. The only way to fix it is to install either another thermal expansion in the general area of the leaking, or to install a portable thermal expansion tank directly where the leaking is. However, portable units are not aesthetic, and are very new to the market, meaning they can be expensive.

Assuming Wrong

When locating your expansion tank, it should be in the cold water side of the main valve next to the water heater itself. However, if you find the tank in the hot water area, that is okay. While it is recommended that expansion tanks should be on the cold side, there are circumstances where it is placed on the hot side.

General Objectives

Generally speaking, the tank should be drained periodically to avoid the need for any troubleshooting. There are several tests you can perform to check for a healthy water expansion tank. One test is to use an air gauge. With the air gauge, check the pressure to see if it is twelve psi, or pounds per square inch. If the pressure is not accurate, then all you can do is call a professional plumber. A second test regards the release valve of the tank. For a healthy tank, water should squirt from the valve. However, if there is excess water or water residue on the valve, you know the pressure and temperature in the tank is too high. Also, tap on the tank and listen. If you hear that the tank is not hollow about half way through, such as a thud and not a ping, the diaphragm is damaged, and should be replaced by a professional. Another test to make sure the tank is working as it should is taking its temperature—feel for a warm bottom of the tank and a cool top if the tank is healthy.