Expansion Tanks

Not every home has an expansion tank, but if your home has a boiler for heat and hot water, or if you have a particular large hot water system, you probably do have an expansion tank that requires periodic checking and maintenance to insure the essential systems in your home function properly without interruption. Most residential plumbing systems don't require them.

An expansion tank is generally about a 2-gallon sized bucket tank hanging off the side of a boiler and in some hot water systems. They are used to protect the home's plumbing system by absorbing the excess water pressure that can build up when water is heated or when a hot-water faucet is turned off abruptly.

If you live in an older home or have been in a building with steam or hot-water heat, you have probably heard the pipes bang or "hammer" when you turn off the hot water, an effect referred to by plumbers as "water hammer." This is caused by sudden changes in water pressure, and it can lead to damage of water pipes, boilers and the hot water system.

An expansion tank is designed to mitigate or prevent this water hammer effect, and when working properly your boiler and hot water system will function just the way they were designed to do. A hot water expansion tank is generally half full of air and half full of water, with the two sides separated by a flexible diaphragm. As the water heats it expands upwards, putting pressure on the diaphragm, and it in turn relieves pressure in a closed water system. But over time these expansion tanks can wear out, with the diaphragm slipping or breaking, allowing water into the air portion. When this happens the expansion tank is not doing the job it was designed to do — take pressure off the hot water system — and this could lead to damaged pipes.

The plumbing pros at Benjamin Franklin Plumbing of Denver are experts in expansion tanks, boilers and hot water systems generally. If you suspect your expansion tank is not working properly, we can test the expansion tank, repair it, or if need be, replace it and get everything in your system working at its most efficient level.

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