Using t&p valve to drain water heater is bad?

Discussion in 'Water Heater Forum, Tanks' started by pman6, Jul 19, 2020.

  1. pman6

    pman6 Member

    Joined:
    Feb 8, 2012
    Location:
    Los Angeles
    I just did a water heater flush at my rental house today, and had the tenant open the hot water at the sink.

    but the wh was still draining really slowly, until I opened the tp valve, and the water finally started gushing out.

    I kept the tp valve open for 30 minutes while i was flushing and draining.

    any harm in doing it like this every year?


    I don't know why there was still a vacuum even with the sink faucet turned on.
    the wh is on a platform and the drain valve is about waist height.
     
  2. Sylvan

    Sylvan Still learning

    Joined:
    Sep 23, 2004
    Occupation:
    plumbing - fire suppression - boiler inspector
    Location:
    New York
    "
    I don't know why there was still a vacuum even with the sink faucet turned on.
    the wh is on a platform and the drain valve is about waist height."

    Take a take a large bottle and turn it upside side down and you will see the liquid go plop, plop, plop STARVING for air

    Now place a small hole on the opposite side and the liquid will flow faster ax now your not creating a vacuum lock

    On high rise buildings when the unknowing open a valve in the basement and do not have a vacuum relief valve by a tank 40 stories up the tank will implode

    The NBBI and ASME all suggest to test the T&P at least once a year some codes suggest more often

    Actually the "Blowdown valve" located o the bottom of the tank should be opened at least once a year to get sediment out of the bottom of the tank so it will not hinder the efficiency of the heater.

    The sediment and mineral deposits act like an insulator
     
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  4. phog

    phog Active Member

    Joined:
    Jul 29, 2017
    Location:
    Rochester NY
    The heat trap device inside the water heater connection nipple could be restricting things. Nothing wrong with using the T&P like you describe except for the possibility that you're sucking debris into it & it might fail to seal afterward. You could probably cure that by blowing some water out of it after the flush (with tank under pressure). You could also try using a faucet in the cold water plumbing as air inlet instead of the hot faucet. The way the heat trap nipples work is different between the hot and cold lines & the cold might work where the hot didn't.
     
  5. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    That would be a bonus reason to use the T&P valve. It is much better to find that the T&P valve sticks while you are doing maintenance than to have it happen when you don't notice. That is why tests are recommended: does it open, and will it close back?
     
  6. pman6

    pman6 Member

    Joined:
    Feb 8, 2012
    Location:
    Los Angeles

    this is a bradford white wh.

    debris... oh is that why the internet discourages using the tp valve to drain the w.h?

    The tp valve is at the very top of the w.h, so if i drain the water a little from the bottom and then open the tp valve, it should not suck in deposits.


    as for the w.h draining slowly, i'm pretty sure the opened kitchen faucet was higher than the w.h drain valve, so i expected the wh would drain faster.
     
  7. phog

    phog Active Member

    Joined:
    Jul 29, 2017
    Location:
    Rochester NY
    Debris getting sucked into the T+P valve would be more like cobwebs and whatever else is inside the external discharge tube. Not stuff already inside the tank.

    Whether an open faucet is higher or lower than the tank would have little to no effect on allowing air inlet during a drain/flush.

    By the way, many people flush the tank under pressure -- just attach a hose to the drain cock, run the other end into a sink or other drain, and let 'er rip. The pressure can help force out sediment. (Many schools of thought on this way vs. turning off the supply, I have no opinion on which way is "better")
     
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