Quote:
Originally Posted by villagetinker
Check your expansion tank, as stated above, if the expansion tank becomes full of water, there is no place for the heated water to go when expanded, and it will open the pressure relief valve. One other item, if you have hard water, the mineral deposits will eventually stop the pressure relief valve from properly closing, resulting in a slow continuous drip.
Hope this helps, and let us know what you find.
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Excellent explanation. The expansion tank has an air check valve which allows you to check the pressure in the expansion tank. The tank pressure should be set to equal the pressure on the house water supply, usually 40 to 60 psi. When the expansion tank fails (usually in 7-10 years) the rubber bladder within the tank passes water and eventually displaces the trapped air. As villagetinker says above the failed expansion tank no longer functions as a shock absorber. Replacement expansion tanks are available from HD or Lowes for $40-50, and like so many things in life, it's an easy fix if you have the experience and confidence. Keep in mind that a failed expansion tank that's full of water is heavy.
Not every domestic hot water system in TV has an expansion tank. Some plumbers opted to install a pressure relief valve in lieu of the expansion tank on the cold water inlet pipe above the hot water tank which drains outside of the house. The code allowed for either approach. This pressure relief valve is not to be confused with the one that's installed in the side of the hot water tank.