Help diagnosing TPR

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by pattonjg, Jan 15, 2005.

  1. pattonjg

    pattonjg New Member

    Jan 15, 2005

    I am trying to determine the cause of my water heater pressure relief valve engaging. Details:

    50 gallon gas Braford-White (12 years old)

    House water pressure is 60 PSI after reduction by the house pressure reduction valve.

    Before the water heater starts heating the pressure in the tank is 60 psi.

    The heater has an expansion tank.

    Once heating begins the pressure in the tank creeps up to 150 psi and the tpr engages.

    About two cups of cold water is discharged.

    The temperature dial is on the Hot mark with plenty of room to increase the htemperature.

    Could this be a bad thermostat allowing the water to heat too much before it shuts the flame down? I've ben slowly dialing the setpoint back but still am having the problem.

    Any other possibilities or things I should check?

    Thank you in advance for any ideas.

  2. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona

    The expansion tank is not functioning, either because it has lost its air charge or a valve to it is closed, (if you have a valve on the tank).
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  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    Or, the bladder in the expansion tank is shot...rap on the expansion tank. It should sound hollow on the end away from the opening to the pipe. My guess is that it is full of water and there is no place to expand as it heats. If the bladder is okay, it needs some air. You need to check the tank with the water turned off and a faucet open to relieve the pressure. You can use a tire pressure guage to see what is in the tank. My bet is that you get water out of the valve because the bladder is shot.
  5. pattonjg

    pattonjg New Member

    Jan 15, 2005
    Thanks for the suggestions. I'll check it out tomorrow and let you know what I found out.

    Thanks again!

  6. pattonjg

    pattonjg New Member

    Jan 15, 2005

    You were spot on. The termal expansion tank sounded like a rock when I tapped on it and water shot out when I put the tire gauge to it. Off to Home Depot!

    Thanks again

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