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If you have a hot water
heating system in your home then you probably have seen the 2 gallon
bucket size tank hanging off the side of your boiler. You will also find
them hanging off of your domestic hot water system too.
How Hot Water Expansion
Tanks Work
Hot water expansion tanks are
used to protect your home’s plumbing system by absorbing the excess
water pressure that can arise when the water is heated or when a hot
water faucet is turned off abruptly. |
Also, if you live in an old house you might be familiar with a banging or
hammer sound when you turn off the hot water faucet. This banging sound is
due to a sudden change in water pressure and is known as water hammer. Hot
water expansion tanks prevent this water hammer effect that can lead to the
potential damage of your hot water heating system or domestic hot water
system.
| A hot water expansion tank is usually about half full of
air and half full of water. The air and water are separated by a
flexible diaphragm. As the water is heated the water expands upwards
putting pressure on the diaphragm. This pressure pushes the diaphragm
upwards into the air portion of the tank, thus relieving the pressure in
the closed heating system. The process works exactly the same for the
domestic hot water system. |
Photo By Mark Donovan |
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Troubleshooting a Hot Water
Expansion Tank
Over time expansion tanks wear
out. Typically the diaphragm breaks and water works its way into the upper
half of the tank. When this happens the expansion tank fails to operate
properly. When this occurs your hot water heating system or domestic hot
water system are at threat of being damaged due to high pressure in the
systems and water hammer effects. |
You can determine if you
expansion tank has a problem by tapping on it. It should sound hollow about
half way up. If it does not, and instead you hear a thud sound when you tap
on the upper half, then the expansion tank’s diaphragm is probably damaged
or not working. In addition, the tank should be warm on the bottom and cool
on top if it is operating correctly.
You can also use an air gauge to
check the air pressure in the tank. Expansion tanks should have a pressure
of 12 psi. If the pressure is low, you can try pumping it up and checking to
see if it holds. Even it if does hold its pressure initially, it is more
than likely temporary and you should seriously consider replacing it.
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Another possible sign that the
expansion tank has failed is if the pressure relief valve on the boiler
begins to spurt water. This tells you that the pressure in the hot water
system is too high, which could indicate that the expansion tank has failed.
Though they look like a larger
static object that just hangs off your boiler system with no real purpose,
expansion tanks indeed do play an important role in protecting your hot
water heating system and your boiler. Consequently, it is a good idea to
periodically check your boiler’s expansion tank and make sure that it is in
working order. If it is not, consider calling in a plumber.
Additional Home Plumbing Resources
Expansion Tanks from Amazon.com
