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Drip coming off a pressure relief valve on water heater?

Its an A.O. Smith 50 gallon that the relief valve was replaced after 7 years and now the new one is dripping for the last 10 days. No back flow/check valve on main line coming into the house. No expansion tank on water heater. They added a bathroom have a jacuzzi but same amount of people same usage. They said it happens when they use a lot of hot water (i.e. dish washer washer machine jaccuzi) but not always. Heard maybe need expasion tank but want to see what else is out there and if anyone else has had this issue. This my second time seeing this but previous time was with 75 gallon high efficiency. Any suggestion?

Comments

  • danitheplumber
    danitheplumber Member Posts: 84
    Hhhmmm... water hammer... I hear... will see... thanks
  • Eric_32
    Eric_32 Member Posts: 267
    Check the pressure while it's heating up using a screw on pressure gauge off the drain, and check the temperature of water at one of the faucets in the house when it shuts down.

    It's one of the two.




  • Jamie Hall
    Jamie Hall Member Posts: 19,147
    Might be water hammer... but, when you stop and think about it, if there is no check valve on the inlet to the hot water tank (is there?) there is no way the pressure in the tank and piping can rise above the pressure in the rest of the house. If there were a check valve or a pressure reducing valve on the house inlet (there might be) that could do it too, though. In which case an expansion tank is the way to go. Doesn't have to be that big.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • danitheplumber
    danitheplumber Member Posts: 84
    This is in Plainveiw NY if that makes a diffrebt . Also would help to upgrade the water heater to a larger one?
  • icesailor
    icesailor Member Posts: 7,265
    Don't count on their being no backflow/check valve on the water service. Federal EPA Law under the Clean Water Act requires that municipal and public/private water systems be protected from backflow from individual services. That's why all codes require backflow devices on all outside sill cocks that you can put hoses on or irrigation systems.

    Newer systems may have a check valve device outside in a meter pit, if the meters are outside. They may now have meters that have the checks that will fit between meter setter fittings. Or actually inside the meter. Have they installed the radio meters in your area? They might have them installed.

    If you have a house that has absolutely no faucet drips or water loss, you might notice that on occasion, there will be higher pressure, a "Squirt" when you first turn on a faucet. From thermal expansion. There are available, pressure gauges with a second pointer that will record the highest pressure it "sees" during a cycle. Put the gauge on the water service as close to where the service enters the building. Record the pressure and set the monitor needle. Best to set it at 5:00 AM when the system is used the least. Check it 24 hours later and continue to do so. If you get more than a 10# spread, you may be getting outside surges. If the system static pressure is more than 65 or 70#, and you are at the end of a system, you can get surges from anywhere in the system.

    Remember, a check valve will let the pressure IN but not back out. You probably need a pressure tank for services and a PRV.
  • WillieJ
    WillieJ Member Posts: 15
    My unregulated pressure is 135#. I'm at the bottom of a hill. When my regulator was going bad it would creep, allowing pressure to gradually increase. I had drip from the PRV on the water heater and a whoosh of pressure when I first turned on a faucet along with water hammer when I shut a faucet off.

    A new regulator solved the issues, and last time I replaced the water heater, I included an expansion tank which is now code in my area. The expansion tank has solved the last bit of remaining water hammer.

    The expansion tank is easy, just mount it on a tee on the inlet side of the hot water tank.
  • Jamie Hall
    Jamie Hall Member Posts: 19,147
    Ice is right -- a surprising number of structures with municipal water supplies have either a check valve or a pressure reducing valve or a backflow preventer on the supply. If they do, an expansion tank for the hot water is a very good idea, as much on general principles as anything else.

    Most well water supplies don't need it, for the simple reason that almost all well water supplies have a pressure tank (expansion tank) already installed to control the pump.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • icesailor
    icesailor Member Posts: 7,265
    edited October 2014
    "" Most well water supplies don't need it, for the simple reason that almost all well water supplies have a pressure tank (expansion tank) already installed to control the pump. ""

    The "pressure tank" doesn't control the pressure in the system, the Pressure switch does that. The Range/differential setting controls the pressure in the system. The pressure rank determines how much water can be pumped during a pumping cycle. The pressure tank usually has a cross tee fitting that the pressure switch connects to and a 75# pressure relief valve connects to. The residential tanks are rated at 75#.

    A common 1/2 HP, 240 volt 4" submersible water pump that is rated to pump 12 GPM, At 0", 10' or 150'. At 200'. the volume of pumped water may only be 8 GPM. Because at a certain point, the pump must be capable of pumping the desired pressure in the structure. Most submersible water pumps will pump higher pressures with lower GPM's because of the increased number of impellors or "Stages". To get higher pressures (elevations/Altitudes), you need more stages to get the pressure but you sacrifice volume.

    The latest rage is Variable Speed Motors and constant pressure.

    Look at this chart/pump curve for this pump. Look at only a 1/2 HP motor. Notice how the head pressure and delivered volume drops off the h you need to pump the water and add pressure. You need more nuts to get more pressure.

    http://www.femyers.com/ResidentialProduct_my_ws_4s_Predator_PLUS.aspx
  • Jamie Hall
    Jamie Hall Member Posts: 19,147
    I beg to differ -- in part. It is quite true that the pressure switch determines the on and off pressures for the pump -- but it is the size of the pressure tank which controls the length of the pump cycle. I have seen a surprising number of pumps destroyed by not having the proper sized pressure tank (too small).

    I was a well driller/submersible pump installer in a previous incarnation, for what it's worth...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Bob Bona_4Zman
  • Paul48
    Paul48 Member Posts: 4,469
    If there's a PRV or pressure reducing valve, it is a closed system, and requires a potable water expansion tank.
  • FB
    FB Member Posts: 31
    And when you install that expansion tank, isolate it with a ball valve for the day it fails and starts to leak.
  • 4Johnpipe
    4Johnpipe Member Posts: 477
    This picture is from a 4 year old water heater. it sort of made its own check valve...
    LANGAN'S PLUMBING & HEATING LLC
    Considerate People, Considerate Service, Consider It Done!
    732-751-1560
    email: [email protected]
    www.langansplumbing.com
  • icesailor
    icesailor Member Posts: 7,265

    I beg to differ -- in part. It is quite true that the pressure switch determines the on and off pressures for the pump -- but it is the size of the pressure tank which controls the length of the pump cycle. I have seen a surprising number of pumps destroyed by not having the proper sized pressure tank (too small).

    I was a well driller/submersible pump installer in a previous incarnation, for what it's worth...

    I guess that maybe we are saying the same thing. But regardless the size of the pressure tank when new, it controls the pump cycling through the pressure switch. If you flush a toilet and hear the "whoosh" of the pump cycling on and off because the air charge is missing out of a pressure tank, the pump is dying from overacting. It either burns out the start switch in the motor or burns out contacts in the pressure switch.

  • icesailor
    icesailor Member Posts: 7,265
    4Johnpipe said:

    This picture is from a 4 year old water heater. it sort of made its own check valve...

    OMG!!!

    Another dialectic fitting on a water heater that plugged up because of stray electrical current between the steel nipple (with the plastic sleeve in it) and the copper fitting adapter.

    Must be some seriously funkilous well water there.

  • SWEI
    SWEI Member Posts: 7,356
    I have been told that the length of a dielectric separation matters. A couple of feet of (appropriately sized) polymer pipe will give far better galvanic isolation than any dielectric can.

    Some water just really needs treatment.
    icesailor
  • danitheplumber
    danitheplumber Member Posts: 84
    Has a lawn sprinkler with dual check valve back flow on the cold line causing the relief valve to go off