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Thread: Is this normal behavior? - Hot Water Tank Pressure Release Valve

  1. #1
    DIY Junior Member plumbingnewguy's Avatar
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    Default Is this normal behavior? - Hot Water Tank Pressure Release Valve

    I have a 2 year old Rheem Professional Guardian Pro (40 gallon size) - I decided to turn the temperature down on the hot water tank (It was on Setting B - Setting C is "Very Hot and I'm putting to set it to Setting A or the setting before) last night. This afternoon, I had to grab something downstairs about 20-30 min after my wife took a shower. The tank was still re-heating, and the pressure release valve had dripped a bit (I'd say maybe 40-50 ml? It was just a minor drip) onto the floor near the drain.

    Is this normal behavior? Maybe it does this at refill all the time and I haven't noticed? I've never really checked. I just thought it a bit unusual since I'd just decreased the temperature setting is all. Figured I would ask you guys since you've put my mind at ease before.

    Err, I should add that we had to shut the water off a couple days ago to replace one of the stop valves on the toilets and I don't think we reopened the water as far as we normally do, so I wonder if I'd inadvertently been putting too much pressure on the tank that way? Might just be a one off. I re-adjusted the water coming in as well.
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    Last edited by plumbingnewguy; 11-09-2013 at 06:45 PM. Reason: added pic and more info

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    Master Plumber Caduceus's Avatar
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    There is no 'refill' for a water heater. They are always full. As you use hot water from the tank the cold filling pressure pushes the hot water out and the incoming water at the bottom of the tank will be heated. A nice balance of yin and yang in the tank with incoming cold and outgoing hot.
    Anyways, it seems that your water heater may be experiencing a thermal expansion issue, so some questions need to be answered before we go too far. Maybe reading this recent thread will familiarize you with what I'm talking about and use the Q&A parts of the thread to see if you are having similar problems.
    Link for thermal expansion: http://www.terrylove.com/forums/show...ng-from-toilet

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    DIY Junior Member plumbingnewguy's Avatar
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    Quote Originally Posted by Caduceus View Post
    There is no 'refill' for a water heater. They are always full. As you use hot water from the tank the cold filling pressure pushes the hot water out and the incoming water at the bottom of the tank will be heated. A nice balance of yin and yang in the tank with incoming cold and outgoing hot.
    Anyways, it seems that your water heater may be experiencing a thermal expansion issue, so some questions need to be answered before we go too far. Maybe reading this recent thread will familiarize you with what I'm talking about and use the Q&A parts of the thread to see if you are having similar problems.
    Link for thermal expansion: http://www.terrylove.com/forums/show...ng-from-toilet
    Thanks for the info - I believe this might just be a symptom of thermal expansion too after reading your thread. That information provided in your other thread was extremely helpful as well as your insight here. I'm going to monitor things over the next few days to see if it happens regularly, or if it was just a one off. I haven't done or touched anything related to the water's pressure itself as well. Our city has a lot of pressure regulators throughout, and we've never had any other issues here before with water pressure problems.

    I've just started to become a bit more aware of thermal expansion and nuances of the plumbing at home. Naturally, with no knowledge of anything, and the fact that I can't find the owner's manual for my hot water tank, it's a bit of a rough go flying blind without you guys here. Cheers.

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    If you have a 'closed' system, you need an expansion tank to prevent the WH from releasing water when it heats the incoming cold water. If it didn't do it before, when you replaced the toilet fill valve, you may have capped off where that water was being dumped without you noticing (at least it didn't drip on the floor!). That valve is designed to open under either over pressure or over temperature. Unless the thermostat on the WH is defective, it's not over temperature! That valve shouldn't open until the pressure gets to 150psi, which is too high for a residential situation (in the USA anyways, it shouldn't get higher than 80psi before it must be regulated). So, you need to first find out what your static pressure is - if it's over 80psi, you need a PRV. If it only rises when the WH is on, you need an expansion tank. If you need a PRV, you also need a expansion tank.

    Any valve leaking a little bit could mask the high pressure, which may be why you didn't have a leak at the WH until you fixed the other leak that was relieving the excess pressure.

    Also, note that that safety valve on the WH may not reseal well if it has been cycled much...it is a safety device. It's possible it is defective, but once they do open, they don't always work well afterwards.
    Last edited by jadnashua; 11-09-2013 at 08:11 PM.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    In the Trades Gary Swart's Avatar
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    You say you adjusted the incoming water pressure. I am guessing that you partly closed a valve. If that is the case, you did not change the pressure at all. The only way to adjust pressure is with a pressure reducing valve on the main supply line. Valves will reduce the amount of flow, but the pressure will not change. Your problem is almost certainly a closed system created either by a pressure regulator in your home or a newer water meter that has a back flow prevention feature. In either case, you need a thermal expansion tank. Pay attention to the post above from Jim. No need to repeat it here.

  6. #6
    Moderator & Master Plumber hj's Avatar
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    Are you sure it was NOT the drain valve leaking. Sometimes, when you reduce the temperature, the valve "shrinks"internally because it is cooler and that can put less pressure on the sealing washer so it drips a little bit until the valve is "closed" tighter. REDUCING the temperature should not have had any effect on the T&P valve, or thermal expansion.
    Licensed residential and commercial plumber

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    DIY Junior Member plumbingnewguy's Avatar
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    Hello all,

    Just to follow up on this. I wanted to thank you for your advice. I did have a plumber out here and he installed an expansion tank and replaced the PRV (EDIT: It was the T&P valve) on the hot water heater. He also said the hot water heater was now at its recommended temperature setting too.

    After I first brought this up to you guys, there used to be a really high pressured rush of water that came out of the taps that I'd have to bleed the pressure out with to stop the PRV from discharging.

    That appears to be gone with the expansion tank as the plumber said it would, but the shower and bathroom fixtures have remained a bit "stiffer" to the turn after we've showered. The plumber checked the cold water intake at the washing machine, and it was measured at either 52 or 54 PSI, so he didn't feel like there was anything wrong with the water coming into the house. Seems like it only happens when hot water is involved.

    Is there anything else I should be doing here, or is just something I should be living with now? It's fine if this is normal behavior. I wonder if the fixtures were just loose before because of all the sources they had to previously leak out?

    Crackpot theory: A couple weeks ago, a plumber came out and replaced all of our old toilets, and on that same day while he was doing that, I replaced the showerheads in our full baths since they were old and leaking. We also had a slightly leaky kitchen faucet which I replaced earlier in the summer. I wonder if these might have been venting the excess pressure in the past, which was why it was never an issue?

    Anyway, thanks for all your help as always.
    Last edited by plumbingnewguy; 11-24-2013 at 06:12 PM.

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    DIY Senior Member Reach4's Avatar
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    Quote Originally Posted by plumbingnewguy View Post
    but the shower and bathroom fixtures have remained a bit "stiffer" to the turn after we've showered.
    Is that the only symptom that remains?

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    DIY Senior Member Smooky's Avatar
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    I think you are confusing pressure relief valve , pressure reducing valve and the temperature & pressure Valve. (or maybe I'm confused) Here are links to all.

    Pressure Relief Valve
    http://www.watts.com/pages/_products...ls.asp?pid=803

    Pressure Reducing Valve (PRV)
    http://www.watts.com/pages/_products...s.asp?pid=7666

    Temperature & Pressure relief valve (T&P) This valve is installed on the hot water heater.
    http://www.watts.com/pages/_products...s.asp?pid=6961

  10. #10
    DIY Junior Member plumbingnewguy's Avatar
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    Hi Smooky...yes...my terminology is all quite out of whack. I'm sure I have my terms all screwy and mixed up. It was the T&P that was swapped out when the expansion tank was put in. The guy at the office I emailed said the PRV would likely need changing if the pressure was over 75 PSI, but when measured, it sat at 54.

    Wondering now if I still need the PRV to be replaced though as I answer the question below.

    Quote Originally Posted by Reach4 View Post
    Is that the only symptom that remains?
    Yes. The taps are also not as stiff as they were before the tank was added. Heck, I might be overreacting a bit here, but I just want to make sure that all my bases are covered before I move on with everyday life.

    EDIT: Actually one more thing occurs, though I was told by the plumber to expect it. The excess hot water assumedly from the expansion tank comes out of the taps when I open them. There is a bit of a pressure spike that water comes out, but again, not as crazy as pre-expansion tank. Things go back to normal within a few seconds.
    Last edited by plumbingnewguy; 11-24-2013 at 06:16 PM.

  11. #11
    Retired Defense Industry Engineer jadnashua's Avatar
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    Water doesn't compress, so prior to your addition of an expansion tank, anything that could expand, did when the water was heated. So, yes, you would get a rush of higher pressure water out. ANd, you're right, anything that leaked, limited the pressure rise. Once you fixed all of the leaks, the weakest thing was the T&P on the WH, and it vented. That pressure cycling on the supply hoses of things in the house can take its toll, weakening any hose in the house. Everyone should turn the water to their washing machine off when not in use...it's a good idea, as when those hoses break, it can create a major problem.
    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 wjcandee's Avatar
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    As to your theory about why this happened now. You apparently had a closed system and the pressure would rise due to thermal expansion when the water was heated. Your expansion tank solved this problem. The reason you didn't notice the dripping from the T&P valve previously was that it probably wasn't dripping; excess pressure from thermal expansion was likely venting through one of the sources that you mentioned that you tightened up or fixed or replaced in the past several months. For example, many people don't realize that excess pressure is sneaking out an outdoor hose bib or some similar fixture that isn't constantly in view.

    You did the right thing to put in the expansion tank, and maintenance of the hot water heater T&P valve is never a completely bad idea:



    That's the funniest video but there are several on youtube showing the aftermath of real hot water heater missile events, and that Allstate video is actually pretty close to the truth.

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    DIY Junior Member plumbingnewguy's Avatar
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    Quote Originally Posted by wjcandee View Post
    For example, many people don't realize that excess pressure is sneaking out an outdoor hose bib or some similar fixture that isn't constantly in view.

    You did the right thing to put in the expansion tank, and maintenance of the hot water heater T&P valve is never a completely bad idea:
    Yes - within 24 hours, I shut the hose bibbs off and replaced the last leaky showerhead. I noticed the T&P dripping 4 days later. It might've started that same day, but I didn't notice it until I was downstairs in the laundry room after my wife had showered.

    Plumber measured the incoming cold water at 52 PSI when they installed the tank Friday, which they confirmed again today meant that the PRV was working properly and wouldn't need replacement.

    I spoke again with our plumber today. The T&P has stopped the dripping as it was expected it would, and all that remains now is that certain bathroom fixtures (the showers and single lever sinks) are a bit tighter/stiffer to turn on, which I've been told is normal in our closed plumbing system in these situations. I can live with that as long as I know it's normal behavior.

    Thanks for your help on this one over the past couple weeks everybody.

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    DIY Senior Member JerryR's Avatar
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    We recently bought and moved into a home built in 1997. We pulled all toilets so we could remove and replace tile throughout the house. Every stop valve leaked so I decided to replace every stop valve with Dahl 1/4 turn compression angle stops on all sinks, toilets etc, 20 in all. What a difference.

    I also had a dripping, rarely used shower head in the pool bathroom and replaced the Moen single Cartridge. WOW what a difference in how easy that one operates compared to the remaining shower and sink handles. I'm now in process of changing every other Moen sink and shower/tub Cartridge.

    I don't know how old your single handle sinks are but you may have the same is issue as I did. They are just old and internally corroded.

    JR
    JR

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    In the Trades Gary Swart's Avatar
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    I suspect the excess pressure was bleed through the old toilets. The water volume bled is really quite small, so it would likely not be noticed in a toilet. Your new toilets have valves that are working properly so the expansion had to find somewhere else and that was the T/P.

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