Hot Water Expansion Tanks help Maintain a Constant and Safe Pressure in your Hot Water Heating System
By Mark J. Donovan
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A heating boiler expansion tank is used to prevent a hot water heating system from over pressurizing. As water increases in temperature its volume expands. If there is no place for the increased volume to go the hot water heating system could fail. Failure could result in a damaged boiler, broken pipes or even worse. In cases where there is a failing heating boiler expansion tank slow faucet water leaks may be observed.
A properly functioning heating boiler expansion tank has a bladder that separates the tank into two reservoirs. One side of the tank contains pressurized air, and the other side is for holding water. |
As water is heated its volume is increased. The heating boiler expansion tank provides a space for storing the increased water volume, thus preventing the hot water heating system from becoming over pressurized.
| Heating boiler expansion tanks are typically located near and above the boiler, although they do not necessarily have to be. Normally they are found either installed below or above the cold inlet pipe or hot outlet pipe, relative to the boiler. They can however be installed at virtually any angle or position.
There are pros and cons for installing them in the various angle and positions. Heating boiler expansion tanks are installed using a large “T” fitting that is inserted into the inlet or outlet pipe path. |
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The hot water expansion tank is then screwed into the open end of the “T” fitting, with some plumbers tape first wrapped around the expansion tanks steel threads.
Temperature and Pressure Relief Valve
In addition to a heating boiler expansion tank a temperature and pressure relief valve (TPR valve) is typically installed in a hot water heating system. The TPR valve provides a final safety check in the event the heating boiler expansion tank fails. If for example, the heating boiler expansion tank’s bladder breaks or the tank looses air, the entire tank can fill up with water.
As a result, water pressure will build up in the heating system. As already discussed this could cause a catastrophic failure of the heating system. The TPR valve is designed to sense the high temperature or pressure condition and open up and spew hot water to relieve the pressure in the hot water heating system. TPR valves are typically connected to a pipe that directs hot water downwards and preferably into a floor drain.
| Heating Boiler Expansion Tanks Testing and Replacement
In cases where the hot water expansion tank has lost air, the tank should be drained and re-pressurized. You can typically use a bicycle air pump to re-pressurize it. Typically the air pressure in a hot water expansion tank is around 12 PSI, however you should confirm the proper pressure with the hot water expansion tank manufacturer. If it is determined that the bladder has failed a new heating boiler expansion tank should be installed. You can determine if the expansion tank has failed by feeling and tapping it. If it is full of water it will feel entirely warm if it is located on the hot side of the boiler system. |
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In addition, if it is full of water it will have a thud sound throughout its entire body when you tap on it. A properly functioning heating boiler expansion tank should normally have a hollow sound on one half of it when you tap on it.
Though simple in design, a heating boiler expansion tank plays an important role in protecting your hot water heating system.
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