Warm water delivered to cold supply lines

Discussion in 'Water Heater Forum, Tanks' started by BigEdgar, Mar 9, 2020.

  1. BigEdgar

    BigEdgar Member

    Joined:
    Nov 21, 2009
    Location:
    Seattle
    Hello,

    I'm having an issue with warm water being delivered to a cold water fixture. Our water heater is in the basement. When I turn on the cold sink faucet in the 2nd floor bathroom, we get about 5 seconds of cold water, followed by about 15 seconds of warm water (85 degrees) and then we get cold water again (50 degrees). I suspect it could be hot water from the water heater backfilling into our cold supply lines.

    Here are some notes and things I've investigated:
    1. The cold water supply lines in the basement leading up to the water heater are warm to the touch. The main lines are copper and it's less evident there, but the supply lines that tee off the main to lead to the 2nd floor supply are PEX - you can feel the heat more clearly when touching the PEX.

    2. I've insulated the pipes around where hot and cold supply lines cross to rule out the hot water pipes heating the cold. This didn't solve the problem.

    3. We've had this same plumbing setup for the last 14 years and this issue only started appearing in the last 6 months.

    4. This issue was present during the summer when we don't use heat (forced air), so it's not related to something like pipes being near a heat vent.

    5. I can't really replicate this situation in other fixtures in the house, perhaps because the other cold water supply lines are farther down the line from the water heater. It seems to be isolated to the 2nd floor bathroom, whose supply lines are closest to the water heater.

    6. The other cold water supply lines in the 2nd floor bathroom seem impacted as well (I measured water at 72 degrees from a sample of the toilet tank). So that rule out an issue with the sink fixture.
    I've diagrammed the setup below in case it's helpful. I'd be grateful for any ideas on what might be going on, or other things that I could do to troubleshoot. Also, if there's any immediate danger with this situation, it'd be good to know that as well .

    Thanks!

    upload_2020-3-9_14-16-16.png
     
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    Most water heaters were delivered with heat traps. IF yours was, and they were installed, the one on the cold line could have failed, and is allowing water to migrate up the cold line via convection.
     
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  4. BigEdgar

    BigEdgar Member

    Joined:
    Nov 21, 2009
    Location:
    Seattle
    Well dang, that certainly would make sense. I didn't know that a heat trap was a thing. Here's a picture of the actual setup and the inlet (cold is on the right in the first picture). A few follow up questions on this:

    1. Would the heat trap be integrated into the nipple, and does that look replaceable based on the second picture below?
    2. A little bit of Internet research also seemed to indicate I could replace the copper flex line with something that I could make a loop out of. That seems like it could be easier than replacing the nipple, but is that a viable alternative?
    Thank you!

    IMG_20200309_160932.jpg IMG_20200309_160910.jpg
     
  5. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    When there are heat traps, they're in the nipples.
    I see some 75 gallon 1" nipples with flaps. The plastic balls they used to have would sometimes wind up floating downstream. What a mess that was.
    I have an instant hot in the kitchen. That gives me a burst of warm water at the sink on the cold side.
     
    MASTERPLUMB777 likes this.
  6. BigEdgar

    BigEdgar Member

    Joined:
    Nov 21, 2009
    Location:
    Seattle
    Thanks, Terry - we don't have any instant hots in our plumbing, so I'm leaning towards the heat trap failure being the likely culprit. Do you think a loop in the copper supply line would be a viable alternative to the mechanical heat trap in the nipple? Or will we have to replace the nipple / heat trap to fix?
     
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    Having an inverted loop on the inlet piping if deep enough, should stop the convective loop.
     
  8. BigEdgar

    BigEdgar Member

    Joined:
    Nov 21, 2009
    Location:
    Seattle
    Thanks, Jim. I tried yesterday to get the nipple off to replace the nipple and heat trap. I knew there was a chance that I could wreck the nipple, and since this water heater is 14 years old, I decided I'd give it the old college try, but if I couldn't get it off I'd consider it a sign that it was time to get a new water heater. I put a 5/8ths inch bolt in the nipple to keep it from collapsing, but this is one of those nipples that's tough to grip without damaging the threads, so I bailed when I couldn't get it to turn and my plumber's wrench started to strip the threads on the nipple.

    I put it all back together and will start looking for a new water heater (wife says I should look at tankless). Thanks again for the help - you guys are awesome!
     
  9. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    1. Does your big copper cold pipe above the thermal expansion tank feel warm? That would indicate this unwanted circulation.
    2. You have a ground bypass wire between your cold pipe and your gas pipe. That doesn't seem right, but I am not sure. Normally such a bypass is between the hot supply and cold supply. That is not causing your water temperature symptoms.
     
  10. BigEdgar

    BigEdgar Member

    Joined:
    Nov 21, 2009
    Location:
    Seattle
    Hi Reach4,
    1. Yes, the big copper cold pipe above the expansion tank is warm and it's backing up into the section that tees off to a pex line that goes to the 2nd floor bath, where this issue is most prevalent. I tried to show that in the diagram included in my first post.
    2. The ground bypass goes between from the gas pipe to the hot water and then to the cold water pipe. You can't see the connection to the hot water pipe in the photo, but it's there.
     
  11. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    I had lost track of that diagram. A spring loaded check valve in series with the shut off valve in your diagram would stop that hot cold, but I think that would be hard to pipe in.
     
  12. BigEdgar

    BigEdgar Member

    Joined:
    Nov 21, 2009
    Location:
    Seattle
    Hmm... The spring loaded check valve is an interesting idea. It would be easy to install one on the end of the flex copper line that feeds the WH, but I'm betting that it's not safe to install the check valve between the WH and the expansion tank on the cold side (city water / rest of cold system --> check valve --> expansion tank --> WH).
     
  13. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    You are right that the expansion tank must be on the WH side of the check valve. Click Inbox.
     
  14. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    Probably the easiest thing to try would be to get a longer flex pipe and run it in a loop. The extra pressure may slow the convection down. WIthout anything to stop the convection, it can work its way all the way up the pipes.

    New WH will come with a check valve on both the hot and cold lines. Make sure to install them on the proper sides, or you'll not get water in or out!
     
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