Water heater pressure relief valve let out some water. Not sure if I should be concerned

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by pman6, Dec 10, 2016.

  1. pman6

    pman6 Member

    Feb 8, 2012
    Los Angeles
    Just wondering if this sounds like something that would concern you...

    Tenant increased the gas water heater temperature on the thermostat recently because she wasn't getting hot water fast enough in the bathroom furthest away from the water heater. It's about '5 minutes' past the optimal temperature line marked on the dial.

    Water is nowhere near boiling hot, but I'm wondering if that's enough to cause the TP valve to open.
    It let out a small puddle of water.

    Does this sound like normal function to you? I mean if someone turned the dial all the way to HOT, would the TP valve open frequently?

    There are no shut off valves or expansion tank on this water heater.
    I'm in los angeles county.

  2. DonL

    DonL Jack of all trades Master of one

    Mar 30, 2011
    Rocket Scientist
    Houston, TX
    What is your water pressure ? Are you on city water ?

    You may want to install a expansion tank. The valve opening is not normal, But it is doing its job.
  3. Sponsor

    Sponsor Paid Advertisement

  4. CountryBumkin

    CountryBumkin Active Member

    Sep 4, 2009
    Orlando, FL
    IMO, turning the temp setting all the way to hot should not be a problem. That is still within the operating range of the water heater. It sounds like the TP valve is starting to go bad, or you should have an expansion tank and don't, or if you have a tank maybe it is bad (full of water/no air).
  5. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona
    If it releases a "little water", then it is probably a thermal expansion issue. If it were temperature, it would release a "LOT of water" and do it for an extended time period.
  6. Reach4

    Reach4 Well-Known Member

    Sep 25, 2013
    It may well be that you have a check valve on the water meter or that you have a pressure reducing valve (PRV). If so, you should have a temperature expansion tank.

    You can get a pressure gauge with garden hose connection and a "lazy" / "tattletale" hand that will record the peak pressure. If you get that you may find that the pressure rises after a shower to 150 PSI. The amount of rise will be proportional to the temperature rise at the WH of the water at the end of the shower until the WH flame turns off. Hotter makes more rise.

    Cure is to have an expansion tank installed, and have a shutoff valve put on the intake water at the same time. 1/4 turn ball valves are preferred. http://www.amtrol.com/media/documents/thermxtrol/MC8520_08_14_TXT_Sizing_Chart.pdf has a selection chart at the bottom. You will note that the water heating temperature is a selection factor. Therm-X-Trol is a top brand, but others make decent tanks too.
  7. Gary Swart

    Gary Swart In the Trades

    Sep 1, 2004
    Yakima, WA
    The T/P expansion valve has 2 functions. One is to prevent the tank from exploding if the temperature get too high. That's not your problem here. The other function is to release excess pressure. Excessive pressure is caused by having a closed system. The is when you have a check valve or pressure regulator valve in your system. A check valve will prevent the extra pressure caused by you water heater doing its job of heating. Heated water expands. In an open system (not check valve) this expansion is absorbed by the city main, but in a closed system, the expansion has no place to be absorbed, so the T/P opens and released a relative small amount of water to get the pressure back to normal. This sounds exactly like the situation you have. A thermal expansion tank provide a place for this expansion to be absorbed. It is possible, but not likely, that the T/P valve is faulty.
  8. pman6

    pman6 Member

    Feb 8, 2012
    Los Angeles
    I'll check the pressure again. I checked a few years ago, and i think it was in the 40's. I don't expect it to be different now. There's definitely not excessive water pressure inside the house.

    this is an old Rheem water heater, at least 15 years old. It's been chugging along without an expansion tank for so long.

    Faulty TP valve?
    I opened the valve lever, and it let out a tiny bit of air and a bunch of water. Then I closed it, and no leaks.
    I assume that's normal.

    Also, I definitely do not have a pressure reducing valve. I have one on my own home, but not this rental. So maybe there is a check valve at the meter. This rental was built in 1966, so I would have to dig the dirt in the meter box to see if there is a check valve.

    I just needed to ask if I could defer maintenance, since the TP valve seems ok, and there's no flooding.
    As far as plumbing goes, nothing has changed in the last 15 years in this home, and so far it's been ok till now. I'd prefer to save my money for now if this isn't a serious situation.
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    When you have a closed system (a check valve or a PRV...if your static pressure was in the 40# range, you probably don't have a PRV!), after hot water use, that colder water that went into the tank eventually gets hot, it expands, and because the pipes are not elastic, the pressure can easily spike...the hotter you make the water, the more it expands, which is probably why you didn't notice it beforehand. To me, it sounds like a classic symptom of needing a working expansion tank which gives that heated water a place to go.
Similar Threads: Water heater
Forum Title Date
Plumbing Forum, Professional & DIY Advice Cement Water Cistern Heater Question Yesterday at 7:40 PM
Plumbing Forum, Professional & DIY Advice Surging Hot/Cold Electric Tankless Water Heater Jan 6, 2021
Plumbing Forum, Professional & DIY Advice Rheem ProTerra 80 Gal. Hybrid High Efficiency Electric Water Heater Dec 31, 2020
Plumbing Forum, Professional & DIY Advice Splicing hot water pipe closer to water heater? Dec 31, 2020
Plumbing Forum, Professional & DIY Advice Changing a water CI Radiator on two-pipe system to a hydronic toe kickspace heater questions Dec 27, 2020

Share This Page