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Old 12-31-2008, 12:56 PM   #1
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Testing 12 year old hot water expansion tank?

Does anyone know how I can check to see if my hot water expansion tank is working properly? I'm on my third water heater. The first one lasted for about 8 years, and the second only 4 years?? The hot water expansion tank has never been replaced.



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Old 12-31-2008, 06:55 PM   #2
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Well, if it's a bladder type tank, you simply use a tire pressure gauge to measure the air pressure in the top of the tank. If water comes out when you measure the pressure, then you've got a ruptured bladder.

I think you're misinterpreting the cause of your water heater failures. The purpose of adding expansion tanks was the result of city water utilities installing check valves on their water meters. Prior to the installation of the check valves, thermal expansion of water in the water heater would simply result in is some back flow of water through the water meter.

Water utilities didn't like that idea cuz if there was a fire on your street, and three city fire trucks started drawing water out of the water distribution piping, they could lower the water pressure in that distribution piping below the 12 to 15 psi that your hot water heating boiler operates at. The result would be that boiler water would flow into your house's potable water piping, and perhaps into the city's water distribution piping.

By having a check valve on the water meters, then water can't flow back into the city distribution piping, and that protects the city from being sued if the corrosion inhibitor that you use in your heating system ends up in your neighbor drinking water.

So, since water meters have check valves, about the only way to accomodate thermal expansion of water in the heater is by having an expansion tank AFTER the water meter.

A malfunctioning expansion tank won't result in a short lived water heater. It will simply result in the Pressure and Temperature Relief valve on your water heater popping occasionally, spilling hot water onto the floor every time it does.

The most common cause of water heaters not lasting long is their being too small for the family they're servicing. That's simply called being "undersized". You see, the interior of a water heater tank has a powder coating on it called a "glass lining" which is very similar to the "enamel" on steel bathtubs. This coating is brittle and if it cracks, it exposes the steel tank to water, and the tank will start corroding at the crack in the tank's glass lining. So, a crack in the glass lining is the beginning of the end for a hot water heater.

The lifespan of that glass lining, in turn, is determined by the cumulative thermal shocking the lining experiences. When a tank is too small, then the tank will be emptied of hot water every morning when people get up and take showers or baths. The hot water in the tank is then replaced by cold water and so the tank experiences a larger temperature drop every morning than a larger tank would. Also, if you don't regularily flush any accumulated sediment or scale out of a gas fired heater, that sediment or scale can insulate the bottom of the tank from the relatively cool water in the tank. As a result, the glass lining on the bottom of the tank can get much hotter than it otherwise would, and if that happens every morning, that adds to the cumulative thermal shocking of the glass lining.

So, from a tank's perspective, it's better to get a tank that's too big than too small; even though there's more heat loss from the larger tank.


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Last edited by Nestor_Kelebay; 12-31-2008 at 07:09 PM.
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Old 01-01-2009, 08:09 AM   #3
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Thanks, the long showers some family members take could cause this thermal shock. I keep asking them to take shorter showers? Maybe your reply will help my case.

Thanks for the information.
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