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Thread: Water Heater leaking from T&P valve

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    DIY Junior Member misterfixer's Avatar
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    Default Water Heater leaking from T&P valve

    New member here with a small problem at work. This is an electric, 50 gallon WH. New resident moved into a unit, there are 3 adults bathing, washing clothes and dishes. Resident says water is showing up in drain pan of WH. Felt inside of pipe from T&P valve-it was wet inside. Replaced T&P, next day water in pan again. Thermostats are set @ 120F, and checked at faucets - 118F to 125F. Third call out, and the boss says we will replace WH. Guess what??? Water in pan again today. Never have seen this happen with previous residents, or in any of the other 275 units on the property. I understand about thermal expansion, but I cannot figure out how this problem cropped up with the only variable being more residents in this unit. Checked water pressure in this unit, and it read 68psi. Anyone have any ideas, or should I mention installing an expansion tank to my boss?

  2. #2
    Test, Don't Guess! cacher_chick's Avatar
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    Monitor the pressure gauge over several hours, the pressure can change greatly over the course of a day in some areas. Your building might need a new PRV and the expansion tank also.

    Most areas require a licensed plumber to work on multi-family structure plumbing.

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    DIY Senior Member Runs with bison's Avatar
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    Quote Originally Posted by misterfixer View Post
    New member here with a small problem at work. This is an electric, 50 gallon WH. New resident moved into a unit, there are 3 adults bathing, washing clothes and dishes. Resident says water is showing up in drain pan of WH. Felt inside of pipe from T&P valve-it was wet inside. Replaced T&P, next day water in pan again. Thermostats are set @ 120F, and checked at faucets - 118F to 125F. Third call out, and the boss says we will replace WH. Guess what??? Water in pan again today. Never have seen this happen with previous residents, or in any of the other 275 units on the property. I understand about thermal expansion, but I cannot figure out how this problem cropped up with the only variable being more residents in this unit. Checked water pressure in this unit, and it read 68psi. Anyone have any ideas, or should I mention installing an expansion tank to my boss?
    Sounds exactly like what one would get from thermal expansion: more residents (and winter incoming water temps) = more thermal expansion and higher pressure spike. Have you not placed a test gauge on the waterlines overnight? That would have been the first thing to check if the T&P was not actively leaking when you arrived. If you see the pressure spike overnight it will confirm if the T&P is doing exactly what it is supposed to do. Rather than waiting overnight you could fill a tub with hot water until the temperature started to fall off, then allow the water heater to reheat while the gauge was connected. After an hour or two you will have your answer.

    In my own case I discovered that I needed a thermal expansion tank through the above methods after replacing the toilets. The old toilets' fill valves seem to have been leaking down when pressure hit 100-120 psig because that is what I had read on the test gauge several times before that and there were not T&P drips then. After the toilets were changed I noticed some water drips after morning showers. I put the test gauge back on and it confirmed spikes to 150 psig.

    Also, have you considered that prior tenants might never have noticed or cared enough to mention a small amount of water in the pan? I'm amazed at the problems that people will ignore or fail to note.

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    Master Plumber Redwood's Avatar
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    You won't even have to wait an hour or two to see the pressure increase from thermal expansion.
    Just deplete the hot water and watch the gauge climb.

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    DIY Senior Member Runs with bison's Avatar
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    With it being an electric and their much slower recovery time, I hedged. The max temp and therefore max thermal expansion won't be reached until the tank has recovered...although the T&P might begin relieving much sooner than that. There might be some other parts of the system taking up some of the thermal expansion.

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    Master Plumber Redwood's Avatar
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    Here's where the difference from an engineer and an plumber come in...
    One relies on data and the other has watched the pressure gauge climb rapidly many times...

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    DIY Senior Member Runs with bison's Avatar
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    Observations are part of the data. And what I observed with my own T&P was that the pressure rose the whole time the burner was running until the relief pressure was hit. It was near the end of the burner's run when it would relieve if at all. Our usage rate is not high so I'm not surprised by this. But I have to anticipate that others' systems might have higher usage rates and perhaps a slowly dripping faucet or such that would alter the scenario. (It's an example of providing more robust advice rather than simply jumping to a conclusion.) So if one wanted to see this in an electric heater and cover all the bases to determine if the T&P is popping due to thermal expansion the duration would be considerably longer.

    Understanding why and what extremes to look for is the difference between an engineer and a plumber.

    A water heater is a pretty simple case compared to all the scenarios one has to consider for thermal expansion joints/bellows on the shells of 600 and 1200 psig steam process heaters (with superheat cases to boot.) Start up, shut down, failed/stuck control valves or instrumentation, loss of utility side, pump failures, etc. all have to be considered to determine the design case. One has to consider not only unexpected failures, but operator error.

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    Plumber Cass's Avatar
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    It is not necessary to wait till the T&P discharges to understand what is going on unless you want to waste time....

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    Plumber Cass's Avatar
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    Quote Originally Posted by misterfixer View Post
    New member here with a small problem at work. This is an electric, 50 gallon WH. New resident moved into a unit, there are 3 adults bathing, washing clothes and dishes. Resident says water is showing up in drain pan of WH. Felt inside of pipe from T&P valve-it was wet inside. Replaced T&P, next day water in pan again. Thermostats are set @ 120F, and checked at faucets - 118F to 125F. Third call out, and the boss says we will replace WH. Guess what??? Water in pan again today. Never have seen this happen with previous residents, or in any of the other 275 units on the property. I understand about thermal expansion, but I cannot figure out how this problem cropped up with the only variable being more residents in this unit. Checked water pressure in this unit, and it read 68psi. Anyone have any ideas, or should I mention installing an expansion tank to my boss?
    How many units in this building...I would check for a check valve or PRV in this unit, separate from the building...does the building have a PRV or check valve...check the WP over time with a lazy hand pressure gage...leave it on for 24 hrs.

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    Master Plumber Redwood's Avatar
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    Quote Originally Posted by Cass View Post
    It is not necessary to wait till the T&P discharges to understand what is going on unless you want to waste time....
    Of course if i was the type of plumber Bison imagines me to be I'd be sitting there with a clipboard and a stop watch taking pressure readings by the minute to make a pretty graph to present to the customer...

    Personanlly I'd just go and look at the base pressure before running anything to make sure its stable and there isn't a bad PRV.
    Then I'd deplete the tank and close it up watch the pressure climbing hit a faucet real quick to watch it drop once or, twice then.
    I'd go get the parts I need and get on with it...
    No sense in wasting time and the customers money....

    Its a pretty simple system with a simple diagnosis.
    No sense in making it more complicated than it really is...

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    DIY Senior Member Runs with bison's Avatar
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    Redwood should change his user name to Redstraw since all he does is put up worthless strawman arguments. Keep trying Redstraw, you'll eventually score a point. <yawn>

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    Master Plumber Redwood's Avatar
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    Your replies are so...



    I suggest reading my signature...
    Then applying it...

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    DIY Senior Member Runs with bison's Avatar
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    Quote Originally Posted by Redwood View Post
    I suggest reading my signature...
    Then applying it...
    I suggest you read your signature, understand it, then apply it. Of course you always fail at step #2.

    Besides, we already know what you would have really done in this situation. You would have told them they needed to install a new BW water heater...you aren't exactly the sharpest pencil in the box.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Let's make this fairly simple...if the pressure rises without the WH running, there's a PRV problem. If it rises while the WH is recovering, it is an expansion tank problem. You only need to know which situation is occuring and note the trend...the solution is obvious, and easy to fix. Now, an engineer might find it interesting to compare the pressure rise with the volume of the tank and verify the correct size of the expansion tank and see if it correlates with his calculations...a plumber knows what's required to make the customer happy and just does it saving the customer time and therefore money. Once the engineering is done, the customer doesn't need to pay for the experiment whose outcome can be quickly and easily recognized based on his experience.

    Let's keep this from throwing barbs...there's a difference in providing a service at a reasonable cost and and engineering exercise to discover new things. this isn't rocket science, been there, done that.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Senior Member Runs with bison's Avatar
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    Jim,

    My original point, which has been distorted by Deadwood's errant crusade, was to determine if it was thermal expansion. I gave several ways of doing so: passive as in waiting overnight and active as in doing the test oneself by discharging hotwater and monitoring pressure during recovery. Only a simpleton like Deadwood/Redstraw would have to stay by the gauge the whole time. (Even you fell for his strawman claim about what I was saying, nothing is more irritating that having a buffoon like that shape one's image. Just another reason to loath a disengenous scumbag like him.) Afterall, that's what the red needle is for on the test gauge and is how I've used it. Furthermore I went into several "why's" of how this could be happening now but was not observed before. (I could have/should have added that other unrecognized changes such as fixing a dripping faucet or replacing a toilet/fill valve could also reveal the sort of symptoms observed.) This was to answer the OP's question in an inclusive enough way to help him find the solution. I made the assumption that the OP needed a bit more thorough analysis and reasoning based on their initial post.

    A key consideration is how high the pressure is getting. If it's not getting anywhere near 150 then the T&P should not be opening. If it is getting that high then it is either a supply issue, or thermal expansion. Unless the main pressure is close to 150 even a failed PRV wouldn't be the primary culprit although it could very well be a contributor. As it is, the OP probably knows the approximate main pressure for the 275 units already. It is hilly here and in some low lying areas near the water towers/pumps the pressure is close enough to 150 psig that plumbers have commented to me about T&P relief/PRV problems in those areas.

    But what do I know? I'm just an engineer who quickly figured out that the BW pimps' longtime theories on the Flamelock problem weren't accurate much of the time...and also figured out that the shared Unitrol Robert Shaw valve was the culprit in a large quantity of the problems...something that could save a homeowner around $800 compared to following Deadwood's standard "advice." Going counter to some clique's theories is nothing new to me, I've been through these sorts of root cause battles with other engineers and corporate execs before and have the battle scars to show for it. The underlying system doesn't care how we think it works, what matters is whether we interpret the data correctly to understand it and then profit from understanding it. I've had R&D Directors tell me I didn't know what I was talking about with a system that had been running 20 years, then a year later recall that mistake when toasting the success of my solution to a long standing problem, admitting,"You know, I thought you were nuts when you said it worked like this..." I let the data, observations, calculations, and established engineering principles guide me to the root cause and solution, not the opinions of a PhD chemist, MS engineer, master plumber, operator, or mechanic.

    Heck if you want a real laugh, ask Deadwood to regurgitate and interpret the legal boilerplate in BW's comments on water heater jackets. He couldn't reason his way out of paper bag.

    So what really matters is whether or not the OP gets enough of an explanation to determine what is happening and why, not what Deadwood thinks or what I think.

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