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  • T&P valve issues

    My electric water heater is about 3 years old, I noticed that the T&P relief valve was allowing water to "port" out of it and down the drain line, thinking the valve was bad I replaced it but still have the same problem. It only seems to happen after some hot water has been used and the tank is heating up again. Water pressure at an outside hose bibb is around 60-80, the pressure at the tank when it is idle is about 70, when the "leaking" happens the pressure at tthe tank goes up to about 142. Should I be looking at a thermal expansion tank?? Thanks

  • #2
    Re: T&P valve issues

    Yes you need thermal expansion tank

    Comment


    • #3
      Re: T&P valve issues

      The tank should be installed in the cold water supply line before or after the shut off valve and what prevents the tank from filling when the water heater fills? I understand how the tank works for expansion but what keeps it from filling up when the heater does?

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      • #4
        Re: T&P valve issues

        The exp. tank has a bladder inside. Half fills with water other half has pressurized air. Can be installed anywhere on the cold water line but most plumbers install next to heater.

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        • #5
          Re: T&P valve issues

          I only have about 6 inches of PVC coming from the wall until it hits the ball valve, can I "T" into that and install the tank at a 90 degree from the supply line and I should I install a shut off valve to the expansion tank to facilitate servicing etc?

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          • #6
            Re: T&P valve issues

            Does it matter if the expansion tank is installed before or after the cold water shut off valve??

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            • #7
              Re: T&P valve issues

              Originally posted by jw39 View Post
              My electric water heater is about 3 years old, I noticed that the T&P relief valve was allowing water to "port" out of it and down the drain line, thinking the valve was bad I replaced it but still have the same problem. It only seems to happen after some hot water has been used and the tank is heating up again. Water pressure at an outside hose bibb is around 60-80, the pressure at the tank when it is idle is about 70, when the "leaking" happens the pressure at tthe tank goes up to about 142. Should I be looking at a thermal expansion tank?? Thanks

              You should also check to make sure the temp-limiter on the top thermostat is not sticking. sometimes a shorted element or wiring can cause it to stick.....Does the water get real hot and then the heater shuts down?

              Or is it just high pressure only?
              sigpic

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              • #8
                Re: T&P valve issues

                I havent noticed the water any hotter than usual, are there supply shut off valves that also incorporate a backflow preventer?? I am unsure if I should install the tank before or after the shutoff valve, I only have about 4 inches of CPVC on either side of it

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                • #9
                  Re: T&P valve issues

                  Originally posted by jw39 View Post
                  I havent noticed the water any hotter than usual, are there supply shut off valves that also incorporate a backflow preventer?? I am unsure if I should install the tank before or after the shutoff valve, I only have about 4 inches of CPVC on either side of it
                  Never install a backflow preventer on a water heater. that could lock the piping system...if your temp limiter fails and the relief valve doesn't work, the overheated water can cause a explosion of the tank or water sysyem.
                  a backflow preventer will not let the hot water expand back into the system, in case of system failure...

                  You only need a shutoff on the cold side only, not the hot..
                  Last edited by Flowofmoney; 01-13-2009, 07:05 PM.
                  sigpic

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                  • #10
                    Re: T&P valve issues

                    Even a squid can do it, now thats funny!! Well I cut the CPVC and removed the existing shut off valve, I installed a "T" closer to the elbow going down to the heater I rean a small extension of CPVC from teh "T" to the expansion tank and then installed a new shut off valve before the "T". All seems to be working fine ( even though a squid did it ) but my question is now this, Should the charge in the expansion be slightly higher than the operating pressure of the heater to allow the water in the tank to go back into the heater and I am still in the dark as to why this happened to my water heater and nobody elses on my block, could it be something wrong with the heater that would be covered under warranty, the heater is only 3 years old after all. Thanks for all the great advice!

                    Comment


                    • #11
                      Re: T&P valve issues

                      Expansion tank should be charged to the same pressure as the water supply. No, nothing wrong with your water heater that would be covered under warranty. Most likey caused from a change to the water supply system. Either you or the water dept has installed a backflow device on the water line recently. If the relief valve leaked more than a few times I recommend replacing that as well. The spring inside has likely become weak.

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                      • #12
                        Re: T&P valve issues

                        most houses have a check valve in the main water line at the street, so when u use hot water your water heater cools down. when the flow of hot water stops the heater warms the water which causes expansion of your domestic water. this causes an increase in water pressure and in turn causes your relief valve to open up and dump water on the floor. your neighbors might not have this problem because they may not use as much hot water and there tank doesnt get as cold so in turn doesnt build the pressure that your system does or there check valve at the road might not be holding anymore which is no biggie... as far as your expansion tank pressure most resideditial tanks come pre charged with air and dont need to be missed with.... hope this helps

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