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Thread: Just flushed my hot water heater...

  1. #1
    DIY Junior Member jason.w's Avatar
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    Jul 2011
    North Carolina

    Question Just flushed my hot water heater...


    I just flushed my hot water heater and after turning back on the water, I notice the tank was making quite a bit of fuss while filling up - a lot of rushing water. So I checked the cold water inlet and it was wide open. So I left it there and my hot water heater filled up. I was hesitant though that things weren't just right and I opened up the emergency valve (close to the top) and a blast was muddy water came out (into a pot, thank God). Any ideas on what this could be from?

    Also, I notice my cold water inlet valve doesn't seem to be shutting off. I'm afraid that my tank could overfill and explode? Yeah, maybe a little dramatic but I'm trying to err on caution. Could my tank overfill? Also, do I need to keep the water off until I can replace the valve on the cold water inlet?

    Any thoughts? I would appreciate any guidance!!


  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    Aug 2004
    Bothell, Washington
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    If you have an electric water heater, the power must be switched off first.

    When refilling, I open up a tub faucet to bleed air out of the tank. Since there is no aerator on the tub, (most of the time) it's the best place to bleed air out.

    Don't turn the power back on until the tank has completely filled with water.
    If the cold water shutoff on the water heater is not sealing, that's a second job. The water will need to be turned off at the main, and if you are using flex connectors, throw away the old one and use a new one. I never reuse a flex connector.

  3. #3
    Jack of all trades DonL's Avatar
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    Mar 2011
    Houston, TX


    Welcome to Terry's Forums Jason,


    Hopefully it was a gas water heater.

    If it is electric and smells like old stinking socks, then the elements may have got toasted.

    It may have just been air. I don't think that it will explode.

    I guess I am a firm believer that if it ain't broke then don't fix it.
    But sometimes if it ain't broke I fix it until it is.

    Good Luck on your project.

    Theory only works perfect in a vacuum.

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  4. #4
    General Engineering Contractor ballvalve's Avatar
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    Dec 2009
    northfork, california


    If you got that much junk after a flush, you probably didnt do a proper job.

    To really flush it, the valve must come out and be later be replaced by a nipple and cap or a good ball valve. Then, with lots of water running into the tank get your coat hanger or flexible something in the hole and work your way around the base of the tank. Then let the incoming cold run for 5 minutes while you get a beer. This of course means no hose, so you would have to be very creative in a closet.

    I like to use the TP valve as the final flush and not risk getting junk in that moen or delta valve body.... or pull a hot hose off a sink as the drain point.


    A good start for the flush theory.
    Last edited by ballvalve; 07-10-2011 at 02:17 PM.

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    Sep 2004
    New England


    If you didn't turn the power off to the heater while you flushed/drained it, you've probably toasted it. You can only push a little bit of water into the tank unless you've also opened an outlet - otherwise, it justs tries to compress the air in it. It can't raise the pressure higher than your water pressure, so it can't generate enough to affect it - otherwise, the water pressure itself would have done it already. If you got a lot of rust out of it, it may be on its last legs. If it was say mud, then a good flush won't hurt it. The debris going out the T&P valve at the top may make it hard for it to reseal, but if you get the tank full and flush through that until clear, you've got a chance you will flush the crud out of it. It might be a good time to take out the sacrificial anode rod and replace it. They're relatively cheap, and replacing can extend the life of the heater (unless it is too far gone in the first place). They're often quite tight, and may require a really long wrench or an impact wrench to remove, though.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6
    DIYer, not in the trades LLigetfa's Avatar
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    Feb 2011
    NW Ontario, Canada


    Quote Originally Posted by jason.w View Post
    Also, I notice my cold water inlet valve doesn't seem to be shutting off. I'm afraid that my tank could overfill and explode?
    Normally that valve would be full open during operation so your overfill theory is without merit. The tank needs to be and normally is 100% full so there is no space for any overfill.

    I have draincocks on the house plumbing in the crawlspace that can drain the entire house. It makes for a very good place to flush the lines from.

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