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Thread: Specific question about static pressure gauge reading and what it says about flow

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    DIY Junior Member Robert33's Avatar
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    Default Specific question about static pressure gauge reading and what it says about flow

    In the context of troubleshooting the cause of reduced hot water flow throughout the house after a new water heater installation, do equal hot/cold static pressure gauge readings, taken at faucets just a few feet away from the heater, constitute evidence that nothing about the heater or its installation could be the cause of reduced hot flow?

    Thanks.

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    DIYer, not in the trades LLigetfa's Avatar
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    Static pressure readings do nothing to ferret out flow restriction issues. Reduced flow could be from heat traps on the new HWT. Sediment can jam them up.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    With no flow, connecting a fire hose and a straw, both would have the same pressure, but there would be a huge difference in their ability to flow once you turn their valves on.
    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 Junior Member Robert33's Avatar
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    Thanks guys, it makes total sense to me but I wanted some experienced corroboration.

    I've been having a three-way dialogue between a big box retailer from whom I bought the tank and who seems very interested in my satisfaction, and the plumbing company who installed it. The plumber came back out with a rep from the retailer and I foolishly failed to question the above "evidence" when I had the chance, needing time to ponder on it. Foolish should be capitalized considering that the test that was run just prior was to bypass the water heater by running the cold into the hot line which seemed to restore flow. I would have thought that test would be pretty conclusive but apparently I'm easily distracted by shiny objects (pressure gauge).

    If I run the cold line into the hot again, myself, (and this time take precise fill measurements) to to try to eliminate the water heater as the cause, are there any gotchas I should look out for before trying it? Looks straightforward enough (shut off water, make connection, turn on water) but I did notice the plumber grabbing the pressure release valve at some point. Total noob here.

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    DIYer, not in the trades LLigetfa's Avatar
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    When the plumbing is drained to install the HWT, sediment in the lines get disturbed when the water gets turned back on because of the sudden in-rush. This sediment then binds up one and/or the other heat trap, the result of which is reduced flow. This is not uncommon.



    If you can get good flow out the draincock, then the heat trap on the hot outlet is the likely culprit. That is less common with a new HWT but more common with an old HWT where the system has been drained for other plumbing work. The sediment collects in the bottom of the HWT and gets churned up when the water is turned back on. This has happened to me more than once.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    If there was a lot of crud in your supply lines, you may need to go to each faucet and fixture, remove the aerator and clean it out. Some devices have inlet filters...those could be partically clogged. Or, if they used tape on the joints rather than pipe dope, they may have been sloppy and left a tail, and that's restricting the flow. The heat traps could be installed backwards (upside down) or swapped (hot to cold)...they work essentially as one-way valves, and having one in backwards can severely restrict the flow.
    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 Junior Member Robert33's Avatar
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    Thanks again, guys.

    Since I have a livable amount of hot flow, my goal at this point is to try to eliminate the WH as a suspect which would allow me to sign-off on being a satisfied customer. It seems to me that running the cold into the hot line and measuring flow is the simplest way to do that, no?

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    Moderator & Master Plumber hj's Avatar
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    ""Dynamic" pressure readings tell you whether the pressure is dropping and if it is unbalanced, but there is NOTHING in a water heater installation which would reduce both hot and cold pressures throughout the house. A bad or partially closed main line valve WILL do it, however.
    Licensed residential and commercial plumber

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    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by Robert33 View Post
    It seems to me that running the cold into the hot line and measuring flow is the simplest way to do that, no?
    That would depend on where you make the crossover and how.

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    DIY Junior Member Robert33's Avatar
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    Quote Originally Posted by hj View Post
    ...but there is NOTHING in a water heater installation which would reduce both hot and cold pressures throughout the house.
    Cold is fine. Only hot (flow) was reduced everywhere directly after the water heater installation.
    Last edited by Robert33; 09-13-2012 at 08:57 PM.

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    DIY Junior Member Robert33's Avatar
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    Quote Originally Posted by LLigetfa View Post
    That would depend on where you make the crossover and how.
    I was thinking about this.


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    DIY Junior Member Robert33's Avatar
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    Referencing the above pic, is there any more to it than:

    1. Shut off water at cold inlet
    2. Run hot faucet a little
    3. Disconnect/connect
    4. Be prepared for some stray water

    That's all I can think of that makes sense to me but I'm a little concerned about two things:

    1. Does the pressure relief valve need to be involved?
    2. When this was done by the plumber, I recall being asked to turn on the yard hose at some point before the final connection was made and I'm not sure why unless that takes the place of (2) above.

    Thanks.
    Last edited by Robert33; 09-17-2012 at 11:48 AM.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    The water heater is often in the basement...that means that if you break the connection there, all the water in the pipes above it will drain out. You want to minimize that by opening any and all fixtures that are as low as possible, to minimize the water coming out when you break the connection there. Depending on where you have shutoff valves, you might be able to just shut them off, but if you have an expansion tank, it still will spit out water since it's illegal to put a valve between the WH and it.
    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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    Plumbing Contractor for 49 years johnjh2o1's Avatar
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    I would be more concerned about the connection to the flue.

    John

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    DIY Junior Member Robert33's Avatar
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    Quote Originally Posted by jadnashua View Post
    The water heater is often in the basement...that means that if you break the connection there, all the water in the pipes above it will drain out. You want to minimize that by opening any and all fixtures that are as low as possible, to minimize the water coming out when you break the connection there.
    (Fwiw, one story house, WH in garage).

    Thank you, good to know.

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