Home>Discussions>PLUMBING>Water Heater Temp/pressure valve leak
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johnjh2o
Re: Water Heater Temp/pressure valve leak

As I stated in a previous post if you have a PRV (pressure reducing valve) you need a thermal expansion tank.

John

JLMCDANIEL
Re: Water Heater Temp/pressure valve leak

No clucking , merely an open discussion with all but Dobbs and Pelton being cordial.
Jack

johnjh2o
Re: Water Heater Temp/pressure valve leak
JLMCDANIEL wrote:

No clucking , merely an open discussion with all but Dobbs and Pelton being cordial.
Jack

Jack your right. I learned a long time ago that if you keep a open mind you can learn from anyone no matter what there experience level is. I have had employees with two years in the trade that I I have learned from.

John

MSSP
Re: Water Heater Temp/pressure valve leak

Wanted to know if JoHnJ and JLM and I were all in agreeance about the thermal expansion tank. I have enjoyed conversing with you, Not Bickering just differant thinking. Still claiming to be intenet friends.

JLMCDANIEL
Re: Water Heater Temp/pressure valve leak

Still friends. I will defer to you two on this, I have never had a pressure reducing valve in any of my houses.
Jack

Fencepost
Re: Water Heater Temp/pressure valve leak

If there is any "air dome" at the top of the tank, that air will eventually be absorbed by the water and the dome -- which would be a very minimal volume -- will be full of water. When I was growing up, our well pump system was connected to a non-bladder pressure tank. It required regular injection of air to maintain an adequate "head" to prevent the pump from short cycling. A water heater is no different. To maintain this air dome would require either partially draining the tank periodically, or having some means of injecting air. I believe the idea of an air dome at the top of the tank to provide for thermal expansion is a myth.

As for the expansion tank, if the OP is on a private water system with a well pump and pressurized cold water storage tank, an expansion tank is not necessary because the cold water storage tank will be able to handle the expansion of heated water, unless there is a check valve between the storage tank and water heater. If the OP is on a municipal water system, an expansion tank will likely be necessary since many meters and all pressure regulators prevent backflow into the main.

If the OP indeed does have an expansion tank, it may have lost its precharge. The OP should relieve all pressure in the water heater (shut of the inflow valve and open a hot water faucet) and check the precharge pressure of the expansion tank. It should be equal to the static water pressure of the system. If the precharge pressure is low or zero, the expansion tank may not be able to absorb the expansion of heated water, causing a rise in pressure forcing the T&P relief valve open.

Expansion tanks are usually constructed with a water bladder to separate the water and air, preventing absorption of the air by the water. Even so, expansion tanks may eventually lose pressure through micro-leaks in their snifter valves (rubber is porous). Water heaters require regular maintenance including:
[LIST=#]

  • Flushing sediment out of the tank via the drain petcock
  • Inspecting the sacrifical anode and replacing if necessary
  • Checking the precharge of the expansion tank
  • [/LIST]
    This maintenance should be performed annually (but almost no one does it, myself included).

    You could monitor this pressure rise by attaching a pressure gauge to a hot water faucet, then trigger the WH to begin heating. Do not open any other faucets while it is being monitored. The gauge must be connected before you will see a high pressure: when you attach the gauge and open the faucet the pressure in the system will drop as the faucet body and gauge fill. Water is fairly incompressible; in a closed system with no airspace a very small change in available volume can result in a very large change in pressure.

    Fencepost
    Re: Water Heater Temp/pressure valve leak

    Nobody here has told the OP how to install an expansion tank.

    It should be installed in the cold water line, between the shutoff valve and the water heater. A heat trap with a marble should not be used since it may prevent backflow of pressure to the expansion tank.

    JLMCDANIEL
    Re: Water Heater Temp/pressure valve leak
    Fencepost wrote:

    If there is any "air dome" at the top of the tank, that air will eventually be absorbed by the water and the dome -- which would be a very minimal volume -- will be full of water. When I was growing up, our well pump system was connected to a non-bladder pressure tank. It required regular injection of air to maintain an adequate "head" to prevent the pump from short cycling. A water heater is no different. To maintain this air dome would require either partially draining the tank periodically, or having some means of injecting air. I believe the idea of an air dome at the top of the tank to provide for thermal expansion is a myth.

    .

    Fencpost you are comparing apples to oranges. The non bladder pressure tank is always filled with cold water and will, over time, absorb the air in the tank. In a water heater cold aerated water is introduced and the heating forces the suspended air out of the water. It's basic Physics. If you heat water on a stove let it cool you can even taste the difference between that water and the water that put in in the first place.
    Jack

    Joe
    Re: Water Heater Temp/pressure valve leak

    I installed the expansion tank this past Saturday. The leak has stopped and everything seems to be working properly.

    Thank you everyone for all your help. :)

    MSSP
    Re: Water Heater Temp/pressure valve leak

    Gator12 Glad to hear your leak is over. Post a pic for all to see your work and enjoy some relaxation time. Glad we all could help

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