The T&P Valve on my Water Heater is Leaking

411 plumb Let’s relax a minute and figure out whether the T&P valve is doing its job or, if it needs replacement. There are two ways it could leak and be doing its job. The name of T&P Valve has meaning. “T” is for temperature and “P” is for pressure. The valve is the final safety device that can prevent a water heater from exploding.

T&P Valve Leaks Caused By Temperature

If the water temperature exceeds the boiling temperature of water the water heater could have a steam explosion. So the valve is set to open at 210 Degrees F and if the water temperature in the water heater were to cause T&P Valve to open there would be a fairly large release of water until the water in the water heater became cooled enough by the incoming water to allow the T&P Valve to reset. This would be an instance where the T&P Valve was doing its job and replacement is not warranted. Instead you should look at a failed thermostat that is not turning off at the set temperature, the upper thermostat should also have had the red reset button pop out as the reset button is a temperature activated device. Another problem could be an element that is shorted to ground. The 240 Volt supply is only switched on one side, so 120 Volts from the unswitched side could continue to flow even with the thermostat shut off through at least part of the element to ground and cause heating not controlled by the thermostat. If you were to replace the T&P Valve in this circumstance the new one would do the same thing the problem needs to be diagnosed and repaired.

T&P Valve Leaks Caused By Pressure

Water releases caused by pressure can be a little harder to diagnose and cure. They may be caused by the supply line pressure being too high or, thermal expansion within a closed system. In any case a pressure gauge with a “lazy hand” that screws onto a hose bibb will be useful in diagnosing pressure problems. The “lazy hand” is a hand which is pushed to the highest pressure recorded by the gauge needle and does not lower until you reset it. The first thing to check is the system pressure. By most codes if the pressure goes above 80 PSI. a pressure reducing valve and thermal expansion tank should be on the system.

To test the system pressure make sure the water heater is not heating the water in the tank. Run a small amount of cold water to release the build up of pressure due to thermal expansion or, a failed pressure reducing valve, screw the valve on a hose bibb and turn on the hose bibb. The reading you get is the system pressure. If it is greater than 80 PSI. a pressure reducing valve and thermal expansion tank should be installed. If there is already a pressure reducing valve installed it has failed and requires replacement. If it starts out less than 80 PSI. and slowly creeps higher then you probably have a pressure reducing valve that is leaking and allowing the pressure to increase past its set point and it should be replaced. If the supplied pressure approaches 150 PSI. the T&P will open and flow water as long as the pressure it too high. If you have at this point checked the temperature and pressure and both are within the normal parameters of the T&P Valve yet the valve is still open and flowing at this time replace the T&P Valve. Once this test is resolved you should proceed.

T&P Valve Leaks Caused By Thermal Expansion

Next we have  to test for thermal expansion. Run a lot of hot water. Have someone take shower or take a bath. Watch the gauge as the water in the water heater is heated without running any water in the house and see what happens. If the pressure creeps up while the water is heating it is a sign that the water supply is a closed system and thermal expansion is causing the pressure rise. Generally the discharge of water from thermal expansion is a small amount like a coffee cup or, two. Any rise or, discharge from thermal expansion would indicate a thermal expansion tank should be installed. The thing you are looking at is the water heater is a pressure vessel. Cycles of pressure is taken into consideration of the design but it’s a lot like the nine lives of a cat. You use them and you loose them, there are just so many pressure cycles built into the tank before it fails and a thermal expansion tank absorbs the pressure instead of the water heater. Once this test is resolved you can proceed or, proceed with out using any hot water after the water heater has finished reheating and you have run cold water to eliminate any stored thermal expansion.

The next step is to watch the supplied pressure over a period of time. Leave the gauge on at least overnight without running hot water or, if you have resolved that thermal expansion is not a factor you can use hot water. Frequently at night water companies run higher pressures as they fill storage tanks to be ready to meet the water supply demands the next day. This is where the lazy hand is required so it can record any pressure spikes over an extended period of time. Again, if it goes over 80 PSI. a pressure reducing valve and thermal expansion tank should be installed. Ideally you would run this test for a 24 hour period.

T&P Valve Leaks Caused By T&P Valve Failure

If you have run through these diagnostic tests and determined that the leaking T&P Valve is not leaking for one of the above reasons replace it. Just a side note the actual numbers at which the valve is rated to open at has a fairly wide tolerance so it may open slightly before the rated temperature or, pressure. If the pressure is over 80 PSI. or, over the set temperature there is a problem that requires resolution.

Posted in How To Plumbing Tips, Water Heater Repairs Tagged with: , , , , , , , , , , , , , , ,
52 comments on “The T&P Valve on my Water Heater is Leaking
  1. kyla says:

    what does “run T&P out at water heater” mean? my city inspector wrote that

    • Redwood says:

      It may mean that the drain from the T&P is not installed properly.
      It should discharge to a point where it cannot damage the home or injure someone.
      Ask the inspector to clarify what is required.

  2. miriam says:

    hi, thanks for all the information on the post! i have a strange issue. i have a duplex, thus 2 electric water heaters. recently, i noticed one of the t&p valves leaking, ever so slightly. so i called a plumber and he had me replace both t&p valves on both water heaters. the result: both t&p valves started leaking. so, he replaced them a second time and emptied and flushed both tanks. i should note that both tanks had lots of debris and sediment in them. we flushed them till the water came out reasonably clear. the result: the newer water heater’s t&p valve stopped leaking…for a few days. as of today, both valves are leaking again. the older heater gets about 1 cup or so after each shower/heating cycle. the newer heater, just a few tablespoons.

    the other thing to consider is that a contractor in town busted the city’s water main a short while ago. this conveniently coincided with my t&p valve leaking and put lots of sediment, and crud into my water lines. i called the city to find out if this created any kind of surge in pressure to my line. they assured me that my line has consistently been between 42psi and 46psi (well under the rating for the hot water tank).

    my guess it that the broken water main put a bunch of debris into the water heaters that popped the t&p valves. my question is, after flushing both heaters, and replacing both valves, and city telling me that my pressure is lower than 46psi, what could be causing the leaking?

    one other note: my plumber says that he’s never seen an expansion tank on a residential water heater in our town. he says it shouldn’t be necessary.

    is it safe to just let them keep leaking?

    thanks for your response–

    • Redwood says:

      Hi Miriam,
      Although the debris may be an issue your problem really does sound like a classic example of pressure caused by Thermal Expansion in a closed system. I suspect that you may need expansion tanks installed on the water heaters. Using a pressure gauge to verify that the supplied pressure is low then pressure increases to about 150 PSI when the water heater is reheating after a large use would verify this.

      Thanks for posting your question,

  3. miriam says:

    hi redwood,

    thanks for your response. as a follow up: is it strange that for years i’ve never needed a thermal expansion tank and now i need one? does that indicate some kind of a change in the city’s pressure system (like the installation of new pressure reducing valves)?


    • Redwood says:

      Hi Again Miriam,

      Yes, it could very well be new equipment installed by the city. There is an increasing use of newer water meters that have built in check valves that help prevent cross connection contamination problems in a home from reaching the city water supply. Also if they replaced a Pressure Reducing Valve (PRV) they may have used one that does not have an internal bypass or, they may have increased the water pressure on the water main higher than where an internal bypass is effective. In any case checking with the gauge will reveal where the problem lies.

      If they did supply a new PRV you are fortunate as many water suppliers leave that as a homeowner responsibility.

      I hope this helps you out and answers your question adequately,

  4. miriam says:

    thanks redwood. i’ll try the guage and talk to the city again. i appreciate your help!


  5. Rajesh says:

    Hi Redwood,

    Thanks for creating very informative site.

    I am facing an strange issue.
    I have gas water heater.

    Water is flowing out of the T&P valve,
    if I close the water supply into the water heater, water flow slows, eventually stop in some time.
    but I do not get any water from my faucet(from hot side), I guess air pressure is doing that.
    How do clear this air pressure? and stop it building again?
    I guess thermostat has gone bad and doesn’t stop the stove, when it needs to.

    At this time, I stopped gas to the water heater.

    Please suggest.


    • Redwood says:

      Hi Rajesh,
      If your Thermostat on the water heater is not shutting off that is probably why the T&P is activating. This would be a critical safety item on the water heater and I would recommend getting a plumber to diagnose and repair it before turning it back on. In this case the T&P is all that was preventing the water heater from launching through the roof.

      Thanks for Posting,

  6. Tammy says:


    I have an electric water heater. I am having an issue with the T&P Valve discharging almost every late evening close to midnight.
    It discharges a lot of water and sometimes it overflows the pan.
    This is a new water heater, replaced old which had a hole in it. We have replaced the T&P Valve, but still having the pressure release issue.
    I have gone to the street connection and turned down the valve so it is not all the way open. Unit also has an expansion tank installed on it.
    Plumber not sure what to do about it at this time. He has put the pressure at the same on the unit and expansion tank per manufacture suggestion.
    So you have any suggestions on how to proceed? Is the T&P Valve necessary with having a expansion tank installed also?

    • Redwood says:

      Hi Tammy,

      Sorry to hear you are having plumbing troubles.
      You absolutely cannot get rid of the T&P valve as it is what prevents the water heater from overheating or, over pressuring and exploding when temperature controls fail. Search Google Videos for mythbusters water heater explosion for an eye-full. The T&P always needs to be able to do its job or you enter the danger zone.

      I’m going to wing it and give you a diagnosis that I suspect you will find to be the answer for your problems. Partially closing the valve at the street will not affect the water pressure, it can only cut back the volume of water by restricting the flow. Granted if you were running water in the house the pressure may drop because of the restriction but I would venture a guess that at midnight you probably are not filling the tub doing a load of laundry and watering the lawn, so whatever the water pressure is in the city main is what you have inside your home.

      I suspect the water company is boosting the pressure in your area around midnight as they refill water towers and get ready to meet the water demands of the next day. They work through the night to make sure there is plenty of water available. What I want you to do is pick up the Watts #276H300 Lazy Hand Gauge or one similar to it. They are sold at Home Depot and many other home centers or, hardware stores for around $10 -$15. The Lazy Hand Gauge has an extra hand that is driven by the needle and it will stay at the highest pressure recorded. Screw it onto the drain of the water heater and let it record the pressure. I suspect that you will find the pressure comes up quite close to 150-psi which is where the T&P is designed to open and let out the excess pressure.

      If this is the case you will need to have the plumber install a Pressure Reducing Valve or, Pressure Regulating Valve to lower your incoming water pressure to a safe level. Basically if the pressure goes above 80-psi at any time you should install a Pressure Reducing Valve. A Watts # 25AUB Z3 is one of the more commonly used Pressure Reducing Valves and I would suggest setting it at 65 – 70-psi.

      I do not think that you have a temperature problem which is the other thing that could cause the T&P to operate because you are not complaining about excessively hot water and it seems to happen like clock work near midnight which to me sounds like the water company transferring water in their system.

      The T&P is designed to open when the pressure reaches 150-psi or, 210-degrees F. I suspect the pressure is doing it. The pressure may not need to reach 150-psi on the nose to open it may very well open before that point. Keep in mind these valves are not super accurate as they would then cost a lot of money. they are just accurate enough to provide the protection you need.

      I hope this helps you and your plumber figure the problem out.
      Thanks for posting your comment,

  7. John says:


    Thanks for all the great info. However, I’m still having problems with my hot water heaters (we have 2 because we have a large jet-tub that requires more than 40 gal). Here are the steps we’ve taken so far to stop the water from dripping from the T&P Valves:

    1) Checked that the water pressure is at 80 PSI or below (we are right at 80 on both tanks).
    2) Turned the heat down on both heaters to reduce thermal expansion. This actually worked, but we had to basically turn the water to cold…not functional at this level for showering, dishes, laundry, etc).
    3) We have a Thermal Expansion Tank already installed. The house is only 4 years old, so everything is fairly new.
    4) We have already replaced both T&P Valves, and the new ones still STILL leak. We noticed that the leaking occurs after running fairly large amount of hot water, such as after showering or running the dish washer.

    What should we do next? Are the thermostats bad?

    Thanks in advance for any guidance!


    • Redwood says:

      Hi John,

      To me your story sounds like a classic case of thermal expansion.

      My guess is that if you observed the pressure gauge while reheating after a heavy draw or used a Lazy Hand Gauge, which records the highest pressure reached, you would see much higher pressures. Of course these higher pressures would disappear the moment water is run anywhere in the home.

      If you go to the air valve on your thermal expansion tank and press the center of the valve my guess is that you will find water coming out instead of air. This would be a sure indicator that the bladder in the expansion tank has failed and it is no longer functioning.

      I don’t think it a case of the thermostats because your water did get colder with the adjustment and when the T&P opens for heat related reasons the temperature required to activate the T&P is over 200-degrees F which may have generated a hot water complaint and the amount of water that would be discharged if very substantial with enough being discharged to lower the tank temperature.

      I hope this helps you out,

      • John Scollo says:

        Hello again, Redwood.

        First, thank you for your insightful information. You were spot on regarding a failed thermal expansion tank. A test of the air value resulted in a water gusher as it is completely full! I have since purchased a new Amtrol Term-X-Trol ST-8 (3.2 gal) tank. The tank is precharged to the standard 40PSI. The current pressure throughout the home is 62-65PSI. How do I increse the pressure in the tank to match the house? Also, any other tank installation tips you might have would be very helpful.

        Thanks again,

        • Redwood says:

          Hi John,
          I’m glad that we got you pointed in the right direction.
          Just remove the plastic cap and fill it like you would a tire, However, I would not recommend using an air line of of a tank type compressor as it would be very easy to over pressurize the tank and blow the bladder. It is okay to use the small compressor like the ones outside gas stations that you feed quarters into they pump slow enough to easily control the pressure or, you can also use a hand pump.

          I would set it to match your pressure of 65-psi and measure it with a tire gauge of your own, don’t rely on the one that gets bounced all over the pavement every day to be accurate.

          If you have already installed it on your water heater, shut off the water to the water heater and open a hot faucet to bleed off the water pressure then charge the tank and turn the water back on.

          If you haven’t installed the tank yet I’ll tell you that if the water connection is facing up it won’t be too bad you’ll only hve a little bit of water to catch and be ready for the old tank to surprise you with how heavy it is. If the water connection on the tank is facing down you will catch some water and it may be a little ugly. Be ready for it!

          Glad I could help you out,

          • John Scollo says:

            That’s sort of what I was expecting, Redwood, but I wanted to ask since I’ve never had to replace one of these before. Unfortunately, I’m a limited on space with my current configuration, so I only have room for a 3.2 gallon tank. I probably need a larger one since this unit will have to service two 40 gallon water heaters that are working in tandem. The exisitng thermal tank is only 2 gallons, so I hope this new one will suffice. BTW, the old tank faces down, so this WILL be a little messy!

            Thank you again for your time and expertise.


            • Redwood says:

              Hi John,
              You probably will be fine with the 3.2 gallon tank. If you do end up needing a bigger tank you can always tee into the line and take it remote to a nearby position where it fits. As long as the tank connects in at the point where it is needed the tank still provides the same function.

  8. Vikas says:

    Our gas was cut off so we had to relight the pilot yesterday and today there was huge release.I am thinking may be we increased the temperature on the thermostat.Now there is a continuous leak on the T & P valve. Also what is correct position of the lever on the T & P valve ( up or down )


    • Redwood says:

      The lever pulls out a pin on the valve which opens the valve.
      The valve should close when the lever is released.
      There are two legitimate reasons a T&P valve opens and that is when the pressure reaches 150-psi or, the temperature reaches 210-degrees F. Other than that the valve is bad and needs replacing.
      Without temperature and pressure readings I can’t say whether it has failed or, it is just doing its job.

  9. billy says:

    I’m having problems with my hot water heater also. My faucet in the kitchen is leaking hot water. My cold water doesn’t leak. I turn off the hot water underneath the sink and then the pressure relief valve on the tank starts to leak. I replaced the valve and still the same. My water temp at the sink is about 145 degrees. The tank does not have an expansion tank on it.
    Thanks for your help, Bill

    • Redwood says:

      Hi Billy,
      Are you turning off the hot water at 2 separate valve one on the outlet and on on the inlet of the water heater?
      If so that is making a closed system and the thermal expansion is causing the T&P to open. In any case a thermal expansion tank is probably required.

      Why are you setting the temp to 145-degrees F?


  10. gisela says:


    I have an issue with my water heater…I read carefully your e-mails and simply…got scared!!! It’s 8 pm now on a sunday night and I am biting my nails waiting for monday to call for help

    My case has, as we could expect, similarities with most of the cases:
    1) water heater aprox. 14 years old, AO Smith energy saver
    2) on december-08, ans I just found out now (january-2010) one relative spending Xmas with us simple put the thermostat on the ‘very hot’ setting…it spent almost 13 months on that setting, but we began to notice wirdnesses only last december-09
    3) the reason this relative did that was all to known for us: the hot water in thet bath. run out too quickly…so he decided to’fix it’ without informing me: i would have stopped him for doing so…I had the thermostat set in B, which is somewhere close to 120 degrees, as the manual says is the safest
    4) without knowing about the very hot set, we accidentaly (I was taking the trash out and just passed close to the heater in the garage) noticed that the T&P, one day, at 11pm was leaking profusedly…i’d say that it leaked a cup or two…
    5) that’s when I noticed that the themostat was set in the very hot position
    6) I lowered down to B agai and went asking to every member in the household how/when/who did tah but no one did it
    7) speaking to the wife of my relative a few days ago, she told me that it was her hubbie!! now I know but I fear it’s late…i fear that some damage in some internal element may have occurred
    8) a few days now after I reset the thermostat, I again noticed last friday that the T&P valve was leaking again but way much less that the fisrt time…
    9) today I have been watching it from time to time and in doing that I noticed that the thermostat device itself is very warm, although the exteroior/shel of the water heater itself does not feel that warm..almost room temp. is that normal???
    10) I also hear a whisper in my kitchen faucet and I have to replace the cartridge because it began to leak a little a few weeks ago…I had not been able to find a store selling these Price Pfister parts so I ordered by phone and they are supposed to be here tomorrow
    11) patrt 10 maybe a coincidence?? or it’s related to the water heater un-identified issue
    12) please advise: does it seem to you as a pressure thing? or as a thermal expansion?

    I have to call a plumber to check this out…’yesterday’…but still it would be helpful to know your opinion…

    the t&p valve is connected to a pipe that seems to come out from the top of the heater (a copper pipe) but the valve is not connected to any discharge pipe…so when it is leaking (sounds like it’s boiling water) it sperads the water on the floor

    but the amount is not too much

    how did it worked set on very hot foe 13 months? and not causing an expliosion?

    please help me calm down



    • Redwood says:

      Hi Gisela,
      Stop worrying!
      The T&P is either doing its job or, has failed and is leaking.
      The thing that causes an explosion is when the T&P doesn’t leak and it should be.
      The plumber will figure out whats is wrong.
      It sounds pressure related or, like its a bad T&P to me.


      • gisela says:

        Mr Redwood: plumber came today to check my water heater health issues

        In brief, he was extremely brief!!! Could you believe that he did not check for the pressure inside the wh tank or of the supply line (on any of my outdoors valves (hose)…

        He kept telling me that why instal an expansion tank that will for sure fail due the pressure? better replace the whole thing, to which I agreed, but then when I authorized him, he simply said that he did not have the equivalent to my water heater (he said that it is a power vent one) and because of their pricey condition, they are not held in stock!! so I need to wait till next week…

        He also said that he could not change the dip tube because to spend 185 dollars was not a wise thing to do…so better freeze until we get our hopes for hot water crystallized just when he ‘finds’ the so-called power vent thing…

        He did lower the thermostat a bit more (to the a position) and told me this: “even if you have a pressure problem, the water heater will not explode because the valve is working…just like what you said too, but why refusing to install an expansion tank??? It would have been useful in the mean time and it would be peace of mind…and maybe I would not have to replace the heater after all…no?

        He, without checking the PRV by the heater, said that it had failed…period…and replacing it was the solution…I said ok, but yet…nothing proceeded

        Then he suggested that if i was willing to pay close to 25 hundred for a replacement and expansion tank, why not install a tankless wh????? for which i’d get tax credits..

        so he went from an unwillingness to do a thing to sell me a tankless solution…

        Icalled another 5 stars rated contractor…right after this guy left. They will come on monday noon…I am still concerned and hanging..

        That is all for now..



        • Redwood says:

          Hi Gisela,
          It may be very quick and easy to look at a 15 year old water heater and say there is no way I’m touching that one except to replace it. Sometimes the bad condition is blatantly obvious to us plumbers. With a 15 year old water heater I myself would question the Idea of replacing a dip tube and T&P as being something I could get away with doing in many cases. Simply put even if those parts could be replaced your water heater could rust through tomorrow.

          I am suspect about his quick diagnosis that the PRV had failed without using a gauge. I am also thinking that the pricing for replacing the power vent water heater is on the high side of the pricing scale. Pricing varies widely in different market areas as do the costs of running a business but $2500 for replacement of a power vent water heater, installation of an expansion tank, and replacement of a PRV seems quite high and I suspect that he is trying to up sell you to a tankless water heater using his high pricing.

          I’m not to sure what you are talking about with the u-shaped tube your handyman is talking about. There are two possibilities that i can think of this tube being. If it is a condensate drain which removes the water that condenses in the exhaust of the unit then it should have a u-shaped trap in the tube this prevents carbon monoxide from coming out of the tube. If it is the drain from the T&P valve it should not have the u-shaped bend but should be able to completely drain dry.

          Lets talk a little bit about the contractors you are using and the selection process. When I hear of a handyman playing around with a gas water heater I cringe at the thought. Many states have laws that limit the scope of the work a handyman can perform for good reason, I do not know the laws of your state but, I would recommend using the services of a licensed and insured plumber. Handymen in my mind are good for assorted light jobs around the home such as painting, replacing a door lock, light carpentry, not installing or, working on a gas water heater. When you say 5-Star plumber I’m not sure who’s rating them. There are a number of companies out there that market themselves to consumers as a screening process to guide you to a good contractor. These same companies also market themselves to contractors as a place to advertise and receive sales leads for a fee. There is an obvious conflict of interest here that many of the contractors consider to be somewhat of a shakedown where their rating is bought and the consumer is unaware that the ratings have little meaning. Simply put its advertising plain and simple. When a company has two full pages in every yellow page phone book distributed in your area, heads the contractor listing in every listing service on the internet such as the Super Pages, Yellow Book, Angie’s List and all the others they are paying a huge amount of money for their advertising and ultimately who pays for that advertising? You! Many of these are large nationwide companies or, franchises that have incredibly high overhead which they pass on to you the consumer while tending to really have not much talent except for being masters of up-selling and shying away from doing repairs.

          I would recommend looking instead to the smaller ads, talking to neighbors, friends, relatives and co-workers to find out if any of them have plumbers that they use and are happy with. Sometimes the good old fashioned approach is the best way to find a contractor. Many of the best plumbers around do very minimal advertising and have a large customer base simply from word of mouth referrals.

          You may do well upgrading from a power vent to another type of water heater gaining in efficiency and taking advantage of the tax credits. There is a 30% income tax credit up to $1500 that you can take on water heaters that qualify. Depending on the programs offered in your state there may also be rebates of up to $200 available from the Appliance Stimulus Package programs and if your income qualifies you grants from the Weatherization Assistance Program. These are all federally funded but are administered by the individual states so you have to check the program details in your state to see if you qualify.

          Before jumping in and thinking tankless water heaters are the way to go I would suggest looking at this article click here.

          Another option is installing one of the new ultra high efficiency condensing gas water heaters such as the one at this linked article click here.

          Finally it may also be worthwhile to look at some of the new heat pump water heaters which offer come of the lowest operational costs of any water heater. The Stiebel Eltron Accelera 300 leads the pack in economic operation. You can see all the heat pump water heaters at this link click here.

          Even a solar water heating installation should be a very viable option in your area. I have very little information available on my site for you on that option.

          As you can see there are quite a few replacement options that offer a much quicker pay back on your investment than blindly rushing into a tankless water heater installation. A good plumber should be willing to discuss all the options with you. some of this technology is very new and many plumbers don’t even know about them yet. But a good plumber should be interested in looking out for your best interests and be willing to look at new options to discuss them with you.

          Good luck with your mission and I hope this helps you out,

    • gisela says:


      It’s me again…;) … My life is unbelievable busy for my ‘taste’ 😉 but I stole a few minutes to/from ‘myself’ and here I am e-writing to you/
      First of all, let me thank you, Mr. Redwood, from the bottom of my heart for soothing my “maybe” unfounded fears…I also thank you for the info on the other site that I willsurely visit ’cause I am a fan of solving by my self when the level of complication/tools-required wouldallow me to do so…

      Next, let me apologize for two things: the tremendous amount of mispellings in my fast-written post (I should have checked it out of respect to you all), and secondly, let me apologize for coming back to you so many days later…:-<

      I called upon a handy-man in the neighborhood and he said "it's just the t&p… But I, after reading and reading and…reading, and contrasting the info with now running hot, now cold, water, now nothing, etc etc Icame to the conclusion that it has to be a pressure issue…The t&p will not drip if and when I open cold water just a fine flow and somebody takes a shower or I do the dishes or cook…therefore, certainly, there is a pressure thing…

      So I know now that the expansion tank is a must, and so a prv (although the guys coming in a few minutes to check and repair, say tha usually this county will have a prv close to the meter!! since i did not know any about thm I did not ever c\heck on that

      Also, I was wrong about not having an exhaust pipe for the drippings…there is one right behind the unit, it's copper, and it goes inside the wall and I found out where outside it releases the water…BUT…always a BUT…

      the handyman said that the shape (U-shape) of that pipe, before entering the wall…is wrong!!! That the water out of the tnp should not have to go up any pipe but in a gradually downward flowto whereevr it should…and that maybe, he said he has seen this a lot, bees built some nest in the exterior site, and the pipe attached to the t&p is the responsible for the dripping in my wh area… Yeah, I thought with my mouth shut, but still why should that pipe have any water after all…and so frequently…It's the tnp but something is causing that tnp opens and shuts…and drips…and made me panic once…

      He pulled a small head beneath the actual tnp and water canme out…so he said that the pipe might be clogged!!!!!!!!!!!!!!

      Now we have two issues…BUT with your moral support and ideas…we will get them done!! Or, I should say three issues: now we do not have real hot water but lukewarm…and in the cld setting of faucets, water does not come out real cold but somehow tempered!!! Now is it mr. dip tube??? (I wish I knew what I am talking about after seeing face to face ;);)

      Thanks so very much…feel free to idea-me 😉 Bless you, Mr Redwood. Thanks again



  11. dave says:

    when you test your t & p should water still be dripping or does it take awhile to shut off

    • Redwood says:

      Hi Dave,
      It is often hard to tell if the T&P does shut off completely after testing is because when the T&P is mounted on the top of the unit the flat section of the pipe often retains water and may continue to drip out for a while after allowing it to close. The best thing is to check back later and see if it is still dripping. If it is dripping sometimes opening it and allowing it to slam shut stops the leaking. If the leaking doesn’t stop check the pressure to see if it is high. Replace the T&P if it is bad.


  12. Shaun says:

    Thanks for the helpful information. My situtation is similar, but a little different…
    I recently had a gas water heater (50gal) rust through and replaced it with another almost identical – still 50gal, gas, etc. The t&p valve is opening a few times per day during recovery apparently because pressure is getting too high – I’m not sure why this is new all the sudden with the new heater. Here’s what I’ve done and what I know. There is an expansion tank on the cold supply only a couple feet from the heater. I checked the valve on the bottom and no water came out – still had air pressure (at the time it was higher than the gauge I have which goes up to 60psi). Got a water pressure guage and have it on the drain valve at the bottom of the tank. Normal water pressure looks to be 60-65psi. During recovery (after a shower, etc) the pressure climbs rather quickly up to 150-155psi where the t&p valve opens draining small amounts of water. This evening I shut off the water supply, drained the lines to zero pressure and re-pressurized the expansion tank. According to the label it’s supposed to be charged to 40psi – this is what I set it at. I then turned the water back on and ran enough hot water to force a recovery. The same issue occurred, where the tank pressure climbed to 150psi after 15-20 minutes or so and the t&p valve opened. The tank temp is set at the low side of “warm” – should be well below 120 deg. The thermostat seems to respond OK to changes in temp setting. The expansion tank is an Amtrol ST-12 which has about a 4gal capacity which from what I can tell should be plenty adequate for the system. I never noticed leakage from this t&p valve with the old heater (which I had for about 10 years).

    So – from everything I’ve read, the pressure climb indicates the NEED for an expansion tank – I have one and it hasn’t ruptured that I can tell. Is it possible that the exp tank has failed some other way but that I wouldn’t see water through the air valve? Is it possible that I need a larger expansion tank (of course I’d wonder why when this heater is pretty much identical to the otehr – only difference is the old one was white-rodgers and this is lochinvar). What else can cause this pressure rise?

    Thanks in advance.

    • Redwood says:

      Hi Shaun,
      The expansion tank should be pressurized to 65 psi with the water off and a faucet open while pressurizing the tank.

      • Shaun says:

        OK – I wondered about that. So the idea is that normal water pressure does not fill the tank, only increased pressure due to expansion? Is it best to err just a bit higher than normal water pressure? Lastly, at what point is there a risk of over-pressurizing the expansion tank? Thanks.

        • Redwood says:

          Hi Shaun,
          The Thermal Expansion Tank should match the system pressure.
          The exact match is not critical but, too low will have the tank fill prematurely and may limit capacity, and too high will hold the water from entering until the precharge pressure is reached.

          • Shaun says:

            OK, tonight I drained the water, inflated the expansion tank to about 68psi (just a bit above normal line pressure) and turned the water back on, ran hot water long enough to force a recovery and the pressure again marched back up (within 15-20 min) to 150psi where it begins to come out the t&p valve… Interesting thing is that I checked the pressure of the exp tank as the water pressure was rising and the exp tank air pressure never went above its initial charge pressure of 68psi – should I expect that to rise along with the water pressure if the water were entering the tank? Is there something that can happen to the exp tank to keep it from allowing any water in? Wondering if my next step is to replace the exp tank or if there’s something else going on.

            • Redwood says:

              Hi Shaun,
              Is there a check valve between the expansion tank and the water heater inlet?
              Or, is the PRV located in between?

              • Shaun says:

                No check valve between expansion tank and heater inlet. There is however a mixing valve connected to both in and out ports to cool down the water coming from the tank as desired. This mixing valve is newly added with the new water heater.

                Since my last post, I installed a new expansion tank but not sure what to think of the results yet. I pressurized the tank to 60psi and installed it, turned water back on and ran 10 min of hot water to force a recovery. seemed better at first, tank pressure measured on my guage went up to about 100psi. Then, since my heater temp was set down at the low end of “warm” I turned that up to the mark that indicates approx 120 deg standard setting. Pressure then climbed from 100psi to 150psi and opened the relief valve. During this time, the air pressure in the new exp tank raised from 60psi to 70psi but no higher. Am I wrong to think that exp tank air pressure should equal water pressure?

                • Redwood says:

                  Hi Shaun,

                  It definitely sounds like there is a check valve of some sort holding back the pressure in the tank from being realized at the thermal expansion tank.

                  Since this is a recent install probably the best thing to do is call back the original installer and let them solve it as a warranty issue.


  13. Frank says:

    Really good website, very helpful.
    My friend just bought a house and the inspector recommended a new TP valve. I went to the local score and bought a new TP valve and it was so easy to replace since I just had to cut the CPCV and untread the outlet pipe from the valve. The problem that I had was that after testing the valve at my house it would not stop leaking so I went to the store and bought a new valve. The difference was that I needed to remove a galvanize pipe. While I try to remove the pipe the valve snap and broke from the bottom thread, so now I can not install the new valve since the thread of the old valve is in the outlet. Is there any advice you can give me to remove the thread part from the water heater?

    • Redwood says:

      Hi Frank,

      There are a variety of things a plumber would do in this situation. A nipple wrench which is a tool that grabs inside the pipe and unthreads it is one option. Using a large easy out is another.

      Also many would carefully cut into the broken piece a couple of times with a hacksaw not cutting deep to damage the threads on the water heater. Then break the pieces inward and remove them.

      One area of concern I would have is the overall condition of the water heater and not damaging the threads on the water heater. This can make a small job turn into a bigger one. That is something you have to access each time you go to unscrew a threaded connection. In your case you should have been using a hold back wrench when uncrewing the galvanized pipe connection to prevent stressing the T&P.


  14. tiffany says:

    Hi, I am having problems with my oil burner fueled hot water heater. We had no hot water so we reset it and nothing happened, we called a plumber and he came and reset it and the fire came on and we had water 30mins later. 3 hrs later we went in the basement and it was a small flood condition coming from the t&p valve. Every time the reset button is pressed the t&p valve leaks and we only have hot water during that time. What could possibly be the problem? Is it expensive to fix?

    • Redwood says:

      Hi Tiffany,
      Your problem may be as minor as a burner that needs servicing so it will fire properly and not go out on reset, and needing a thermal expansion tank installed/replaced. Or, it may be more serious where the burner is not shutting off when it should, causing the water to become too hot, which is a dangerous condition. In either case a competent technician should be called to diagnose and make the needed repairs. Once the problem is diagnosed they should be able to tell you the cost of the needed repairs.

  15. amber says:

    Okay, my husband and I are having problems with our electric water heater. Our T&P Valve was releasing gallons of water out of it at a time, when we turned on the faucets it would stop, as soon as the faucets turned off, it would leak again. We got a new T&P Valve but its still doing the same thing and the water heater is only a year old. Any idea what could be wrong?

    • Redwood says:

      Hi Amber,
      It sure sounds like a classic case of thermal expansion causing the leaking. It may also be high pressure but we can easily check to make sure the leaking is only caused by thermal expansion.

      All you have to do is turn off the circuit breaker supplying power to the water heater then run a small amount of water to relieve the built up pressure and turn the water back off. If the leak stops and stays off as long as the water heater is off you have thermal expansion causing the leakage. Once you turn the power back on to the water heater the leaking will start up again.

      If the testing above concurs with the results you see you will need to install a potable water thermal expansion tank on the inlet pipe to your water heater. Once that is done you shouldn’t have any more leakage from the T&P Valve.

      If the testing above doesn’t concur then it is probably a constant high pressure problem and more testing and troubleshooting will be required.


      • amber says:

        So is this what we are talking about?

        • Redwood says:

          Hi Amber,
          I’m not sure what the search results you posted showed for you but when I clicked on it a WaterWorks 2 Gallon Thermal Expansion Tank for baseboard and radiant heating showed. This is not what you would need as it is not for potable water.

          The Watts “PLT” Series or, Amtrol THERM-X-TROL of potable water thermal expansion tanks are a couple of good choices.


  16. Heather says:

    Okay…the other day we discovered that we had no hot water. We checked breaker and it was not off, so we opened door on water heater and then discovered that the single element thermostat had been sparked and was corroded. We went to home depot and bought a new one and replaced it. The water had never been shut off outside but the breaker was turned off. After installing new thermostat, we turned breaker on and we started getting hot water after it had time to heat water that was in tank. Yay! Well my son took a shower an hour later and it was fine…shortly after my husband turned on faucet to brush teeth and he heard water spewing out of water heater. He immediately checked it and discovered that water was spraying straight up from the connection where a pressure relief valve would go if mounted on top, but ours is mounted on the side as well as the water connections. The connection is like a lip and if you look down in it, there is sheet of metal that is rusted with a pin hole right in the middle of it. Why is happening? Is it something we did? And should the unused connection not be capped? We have lived in this house 2 years and water heater was here when we moved in. Not sure of age of water heater. So…with this hole being where it is, can it be fixed or does water heater need replaced? Quick response is greatly appreciated!

    • Redwood says:

      Hi Heather,
      I’m not sure what this connection is and why it would be capped with sheet metal.
      A plug would be more what I would expect if there are 2 locations where the T&P Valve can go.
      Can you tell me the brand, model number and the serial number which will probably tell me how old the water heater is.

      I’ll also send you an e-mail and If you could reply with a decent quality picture of this leaking cap, attached to the e-mail I’d appreciate it.


  17. adrian dean says:

    The pressure relief valve open on my hot water heater even when the water is cold. I replaced the old valve and reduced the pressure at meter. What can I do?

    • Redwood says:

      Hi Adrian,
      What is the pressure setting on the Pressure Relief Valve?
      What is the pressure you reduced to at the meter?
      Did you use a Pressure Reducing Valve to lower the pressure or, did you just partially close a valve?


  18. Rick says:

    Hello Redwood,
    Very informative article. Thank you.
    My T&P relief valve is constantly releasing about a quart every few minutes. Started sometime yesterday afternoon/early evening. Tank temp is 130-140. I don’t have a pressure gage yet. I don’t see any check valve’s or pressure regulators anywhere in the hot water lines before or after the tank. The supply comes into the house, through a meter, then splits to the hot water tank. The meter is a meter only. When I close an inline ball valve before the tank, the PRV closes after 15 seconds. When I open the valve, the PRV immediately starts flowing. Does this mean the pressure from the street is too high? Other ideas? Thank you in advance.

    • Redwood says:

      Hi Rick,
      I’d suspect that it is either high pressure or, the T&P Valve is bad, there really isn’t any way of knowing for sure until you check the pressure. If the temperature was setting off the T&P Valve there would be a lot more than a quart coming out.

  19. chris says:

    I replaced a geyser for a client about two weeks ago.
    I also installed a new prv with expantion valve close to the geyser as the original prv is far away next to the water meter.
    the geyser leaks out of the tp valve with steam.
    I changed the thermostat and then also the tp valve.
    I dont think its the prv as that would mean both are defective.
    I have tested both thermostats and they are good.
    what are the chances that there is a short to earth on the brand new element and the neutral is powering the element ?

    • Redwood says:

      Hi Chris,
      The placement of the PRV shouldn’t make a bit of difference as right after the meter would cover the entire home. I’m not familiar with the Geyser Water heater as they are not sold in the US. Is your leak possibly related to thermal expansion?

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