In the water supply system in a home or business, one of two types of systems exist. The first system is called an "open loop system" where water can expand freely when the water heater is operating. Simply put, when water is heated, it expands and with the "open loop system", this can be done without any damage to the water heater.

The other system that exists is called a "closed loop system". This type of system is created when a water softener, check valve or pressure reducing valve is introduced into the plumbing system. In a "closed loop system", the previously mentioned devices restrict the expanding water from the water heater. The end result of this thermal expansion is the stressing of the water heater tank to cause it to either bulge at the top or the bottom of the tank or to stress the seams of the steel tank to eventually cause it to leak which then necessitates replacement of the water heater.

Another problem that can occur with a "closed loop system" is the discharge of water from the temperature and pressure relief valve that is located either on the side or top of the water heater. The relief valve is designed to dump water when there is excessive temperature or pressure in the water heater tank. If this should ever occur, shut the water off to the water heater, turn off the gas or electricity to the water heater and call a licensed plumber to make the necessary repairs. NEVER REMOVE THE RELIEF VALVE AND INSTALL A PLUG. DOING SO WILL LITERALLY CAUSE THE WATER HEATER TANK TO EXPLODE.

The thermal expansion tank has a bladder in it that will expand and contract in conjunction with the operation of the water heater when a "closed loop system" exists. Although other devices are available to control thermal expansion, thermal expansion tanks are the preferred method by Heffner and Associates.