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Locating Crossover In Large Building

Mike_SheppardMike_Sheppard Member Posts: 666
I have a building in DC, approximately 100 condos, that I believe is experiencing a crossover issue which is causing problems with their domestic hot water. 

@Mark Eatherton I am tagging you because when I did a google search for crossover detection methods I came across the “Mark Eatherton Method”

There are about 20 hot water risers in the building. The return lines come off the tops of the risers. The water heater is on the roof. The main hot water line goes to the bottom floor then splits out to the risers.

The water heater is in the center of the building, with 10 risers on the West and 10 on the East. There is a flow balancing valve on each return line.

The last four risers on only the East side of the building are having issues with either getting zero hot water or having to run the faucet / shower for 40+ minutes until it gets hot. 20 condos total. The rest get hot water fine.

There is a hose connection at the end of the main return line. I often find air stuck in return lines and blowing the air out restored proper return water flow. I bled and got a tiny bit of air. I also tried closing the balancing valves on every return and bleeding out each one individually. Got no air.

I have felt return lines going back and forth between hot and cold. In one apartment I got a lot of sediment out of the bathtub faucet. And also found that the sinks went cold when the bathtub was turned to hot.

I am fairly certain there is a crossover issue here. Problem is there is at least 20 condos that I am going to have to check. Luckily each condo has it’s own individual isolation valve on the hot and the cold.

So as of right now this is my plan -
1. shut hot water off to condo. Open all faucets to drain hot water. See if water stops coming out of hot side. If not, there is a crossover.
2. If condo is determined to have a crossover, start shutting off supply to each faucet until crossover is found.

I would love to hear anyone else’s advice who has dealt with this issue before. I’ve dealt with it quite a few times, but not on this large of a scale. And most of the time I find the crossover was caused at a janitor’s sink with a hose.

Note - I already pulled and checked their recirculating pump. It is working properly. Impeller in good shape.

Never stop learning.


  • Larry WeingartenLarry Weingarten Member Posts: 1,914
    Hi, If you're finding any sediment from taps, that suggests the recirc line check valve isn't working. Examining the sediment might let you know if it's from the water heater, specifically corrosion from an anode. Do you have a Flir One or similar IR camera? It's a great tool for quickly finding cross connections and would work nicely with the #1 test you're suggesting. Also, listening for cross connections can work. What brands of faucets and showers are in place? Some are better than others at creating cross connection problems. About air in the lines, there is a possibility that it's gas from the water heater, if you have a glass lined tank. Properly placed vents or a powered anode will help with that. Also, any automatic machines that tie into hot and cold are suspect. Lastly, people sometimes put a shutoff on the shower arm and use it to shut off the shower. This creates a great cross connection!

    Yours, Larry
  • MikeL_2MikeL_2 Member Posts: 268
    edited October 18
            I was involved with a similar issue in a 5 story, 100 room hotel. We traced the problem to counterfeit repair parts. It turns out the on-site   " engineers " were buying & installing inexpensive shower valve pressure balance cartridges - the 1/ 2 price, non OEM parts were allowing crossover.
  • Mike_SheppardMike_Sheppard Member Posts: 666
    @Larry Weingarten that is a great idea about the IR gun. I didn’t even think of that. I have two on my truck - a Flir 8 and a Flir One for the iPhone.

    the sediment looks like little rocks. They have had lots of water main work going on in the road near the building. 

    I forget the brand of faucets, but I was told that the brand the have had a recall right after the building was built due to faulty cartridges.

    They have a 500 gallon glass lines tank. Anodes aren’t powered but have been replaced. And they have two air vents at the top of the end of the run on the recirculation line.

    Great thinking on the shut off arm. I find that on janitors sinks pretty often.

    Since posting this I have learned they have one apartment that is completely gutted for a remodel with everything removed. The problem started the day they gutted the apartment. So that’s something to check.

    So far they have been doing what I said about isolating each apartment individually and seeing if the hot side repressurizes after turning the faucet off. So far they have found 5 apartments with crossovers. I am going back Friday to do more investigating. 
    Never stop learning.
  • ZmanZman Member Posts: 6,008
    The shut off arm is the most common one I see.
    I am also a fan of the "what changed?" school of troubleshooting, the complete gut remodel does not sound like a coincidence.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Mike_SheppardMike_Sheppard Member Posts: 666
    @Zman the more days that pass the more things that have “changed” pop up. There’s been that remodel. A whole list of apartments who have been replacing their fixtures or having plumbing work done. Now I heard there were people to hydrojetting I’d drain lines the day the problem started. There’s been frequent construction to water service lines in the street next to the building.

    not even sure which direction to go with this one lol. Since it’s all isolated to the last four tiers on the far side I have to believe it is a recirc flow or crossover issue. There’s definitely crossovers that have already been found. But the one tier with zero flow through the recirc line on the riser with a hose attached to it is puzzling. I can’t see an entire 3/4 line plugging up to the point of zero flow. The guy at the bottom of that riser gets zero hot water. He can leave it running for 2 hours and it never gets hot.

    Never stop learning.
  • Tom_133Tom_133 Member Posts: 702
    Perhaps the gutted apartment had a sink valve that wouldn't stop dripping and they tied the hot and cold together with a flex line? I have been through similar things, found a hose connection with a hot and cold feed left on because "it was too hard to remember to turn on when needing it", I have found washer valves allowing crossover. Its not easy, but that vacant unit has got to be the issue!
    Montpelier Vt
  • Mike_SheppardMike_Sheppard Member Posts: 666
    Ended up finding it today. Found one apartment in the middle of a bathroom remodel which started the day this issue began. They were very vocal about their frustration with this hot water issue from the beginning yet didn’t tell anyone they gutted their bathroom the day the problem started.

    Their contractor took the shower head off and put a cap on the end. Then left the shower valve open. Direct crossover. We shut the water off to their apartment and within 5 minutes the building was back to normal. 
    Never stop learning.
    ZmanLarry Weingarten
  • JUGHNEJUGHNE Member Posts: 7,205
    I wanted to mention that but am late to the party.

    All of my copper rough ins had the drop ear on the shower plugged and the tub lookout was all copper with a cap.
    Valve turned on, water turned on. Left on for the finish to locate any nail pokes.
    No hot water yet in the house
  • ZmanZman Member Posts: 6,008
    It is sooo much simpler if they use shower valve bodies with integral stops in multi family buildings. I had the same thing happen a couple years ago. After 10 minutes arguing with the "plumber" on the job, I closed the valve and the problem magically went away....
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
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