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Thread: T&P valve activating on new water heater

  1. #1

    Default T&P valve activating on new water heater

    I live in eastern Oklahoma and our home is approximately 30 years old. When built, they installed the primary electric water heater as well as a 20 gallon electric water heater under the kitchen counter. The smaller heater supplies water to the kitchen sink, dishwasher and washing machine. It started leaking due to corrosion so I replaced it with a 20 gallon whirlpool heate purchased at Lowes. No problem, right! About 6 hours later the TP valve activated. Everything is hooked up correctly and the temperature is set right about 130 degrees. Any ideas? Like I said, its set up exactly like the one it replaced. Maybe the thermostat? Any help is appreciated. Thanks, Greg

  2. #2
    Plumber Cass's Avatar
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    It could be a faulty T&P. Let me ask you a few questions first.

    #1 Where the water enters the house is there a check valve and / or Pressure Reducing Valve?

    #2 If there isn't do you know the incoming water pressure?

    #3 If there is do you have an Expansion Tank?

  3. #3

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    Cass, Thanks for your quick response. I can't give you a good explanation of what is on the system or not or what the water pressure is coming in to the house. I do know that we do not have an expansion tank. I was probably ignorant in assuming that since the old tank worked just fine that the new one would also. Where would I find the check valve or pressure reducing valve? All I see under the sink are where the pvc/cpvc pipe runs through the drywall into the water heater. Give me an idea of where to look and I'll get after it. Thanks again, Greg

  4. #4
    Plumber Cass's Avatar
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    Reread the first question.

  5. #5
    In the Trades Gary Swart's Avatar
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    Cass gave you great advice. If you have a PRV in the supply line and no expansion tank, that is most likely the problem. However, since you just did a straight R&R, and your TP didn't leak before, I would suspect the problem may be in the tank. To be brutally frank, Whirlpool heaters are generally considered to be junk. Brand names that once were considered to be first rate quality, often have sold out to foreign companys and the products now produced with those great old names are just crap. We consumers don't keep up with these changes on products we don't buy frequent, so we get caught. So, first go through the check list Cass gave. Water pressure between 40 and 60 psi, no PRV, then replace the TP and see if you just have a faulty one. If that doesn't do it, then take the tank back.

  6. #6

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    I had a new TP valve and replaced the one in the new heater. Same thing happened again. I'm planning on calling the city (small town so we know most that work for the city) and having them check to see if there is a pressure reducing valve and what the water pressure is coming into the house. I can hopefully give you some more intelligent answers once I get this information.
    The thing that stumps me is why is it that the older water heater worked and this one is having problems? The old model was made by the SABH water heater group out of Tennesee if that helps. Both are the same size tanks, have the same specifications for the TP relief valves etc. The instructions say nothing about an expansion tank. Not trying to irritate anyone, just questions from a plumbing newbie that don't make sense due to my limited knowledge. Thanks again for the input, Greg

  7. #7
    Retired Defense Industry Engineer jadnashua's Avatar
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    The town can probably tell you what the pressure is in your area, but the pressure reduction valve, if there is one, is inside of your house, and you own it. Note, there is one other thing that can make your system into a closed one: a check valve. This could be a separate item, or it could be built-into the water meter.

    You need to find out what the pressure is in the piping...with two T&P valves releasing (don't think of it as a leak - it's doing its job, relieving pressure), it is probably not defective valves (but it could be you got two bad ones in a row, not likely, though).

    When you empty the WH and it gets refilled with cold water, the process of reheating it causes it to expand. If there is a check valve somewhere in the system, the pressure can jump up way beyond where the T&P should open and release it.

    When they installed th enew WH, they may have renewed some components that made better seals, and can't release the pressure, so the weakest point the T&P opens.

    You can buy an inexpensive gauge (less than $10) and screw it onto a hose bib like at your washing machine. You could also probably screw it onto the drain valve of the WH tank. Check the pressure when it is leaking, and again right after running a shower. My guess is that you'll see the water pressure climb while the WH is doing its job.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  8. #8
    Master Plumber Dunbar Plumbing's Avatar
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    Most likely what happened is the old tank's T&P was clogged shut. Happens as quickly as 2 years.

    The city won't correct your water pressure problem....they'll just give you static line pressure and add more pressure at night when everyone is asleep.

    If you do have high pressure then expect to install a PRV on the main line and a Expansion Tank at the water heater.

    I run into the situation all the time where T&P's are opening up before the standard 150psi settings. Some open at 120 on up.


    That's not good when you install a water heater for a customer who refuses the PRV&EXP due to financial reasons and now they have to.
    Read what the end of this sentence means.

  9. #9
    Master Plumber master plumber mark's Avatar
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    Talking same probelms here

    Quote Originally Posted by RUGGED
    Most likely what happened is the old tank's T&P was clogged shut. Happens as quickly as 2 years.

    That's not good when you install a water heater for a customer who refuses the PRV&EXP due to financial reasons and now they have to.

    Its hard to convince someone that they need the thermal expansion tank and all the bells and whistles.....for lots more money....

    especially when Lowes and HD wil just slap them in a water heater....at rock bottom prices with no mention of any of this.

    So I finally just listed all the items down right on my work orders with a check list of yes or no for the customer to sign....

    thermal exp tank yes no

    prv valve

    water heater pan

    at the very least they were informed and warned and it keeps me
    out of the carpet cleaning business...

  10. #10

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    The water line comes in directly from the drywall. There is no kind of valve on it at all except for the cold water shut off to the water heater. If I'm understanding you correctly, I need to buy an inline pressure reducing valve as well as a thermal expansion tank. Does that sound right?

  11. #11
    Master Plumber Dunbar Plumbing's Avatar
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    Yes, when you determine what your water pressure is, not until then.
    Read what the end of this sentence means.

  12. #12

    Default

    I'll buy the guage tomorrow. I'll follow the directions previously posted and let you all know what the pressures are. Thanks, Greg

  13. #13

    Default

    Had the local plumber come check the water pressure today (local hardware store out of temp guages...). It was 45 psi coming into the house. He asked about water temp and I told him I had the thermostat turned all the way down but the water was really hot. We tested it and it was a whopping 150 degrees. So, I replaced the thermostat, put the plastic cover on top of it, put the insulation in place and replaced the cover. Hopefully this will solve the problem. I'm keeping an eye on the temp. right now and will report back as to how everything goes. Thanks, Greg

  14. #14

    Default My ignorance revealed, but why this way?

    I didn't mention this sooner and apologize but it just now dawned on me that this is likely the problem. The water heater is wired just like the diagram in the booklet. However, for some reason, the previous water heater had another electrical line run in from the other side of the cabinet that connected only to the element. From what I'm seeing, this line kept the element firing all the time. I have it disconnected right now and the element was off when the water was very hot, say 140 degrees. I drained quite a bit of water out of the tank to lower the temp. The temp got down to 80 degrees and the element kicked back on. Any idea why this extra wiring was run to the element in the old heater? It seems to be working OK now and the element kicks off when the water temp reaches the appropriate level.

  15. #15

    Default Jeezum crow, this gets wierder and wierder

    The extra line I was talking about, is just a plug thats plugged into an outlet with the electric cord run through a small hole in the cabinet and attached to the water heater. It looks like it was a cord to something. All it says on it is 16/3 type sjo neoprene I unplugged the plug and the line went dead. I don't think I even want to know how this all came about. But, like I said, the mind got to tickin and looks like the problem is solved. Any ideas now after the explanation on what the hell this thing is/was? Its allowed the previous water heater to work fine for the last 9 years but looks like the new heater just couldn't handle it. Thanks, greg

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