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Community and Q&A

Tankless Hot Water Installation

DrLou | Posted in GBA Pro Help on

We recently installed a Tankless Hot Water System (Navien NPE240A2) in a 4500 sq ft home with 4 full baths. A new 3/4″ re-circulation line was also installed. The home also has a Springwell Water Treatment System ( installed upstream of a FloLogic Leak Detection System ( to monitor flow and auto shut off if leak is detected. There are spring check valves installed on both sided of the FloLogic Device. We get continued flow readings of 12 to 21 oz/min even when no faucets are running and one sink delivers hot water at cold water faucet when water is first turned on. The hot water recirculation line was not insulated in the interior walls. We can’t figure out how to identify where flow is taking place in order get get a 0 reading when all faucets are closed. Any help or referral to expert in North Dallas area would be much appreciated…

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  1. walta100 | | #1

    It seem silly to ask but does the water circulating in the loop pass thru the leak detector?
    How long has the leak detector been in place?

    Have you tried shutting off the supply valves to the toilets? They tend to leak into the tank and such leaks may escape notice.


    1. DrLou | | #3

      The recirculation line does not pass through the leak detector but is downstream with an intervening spring type check valve. I will add a schematic...
      And yes, I have shut the supply valves to the toilets...
      Thank you for your thoughts and input...

  2. canada_deck | | #2

    If you can draw even a very basic diagram (even just on paper and take a picture,) I think that will help people to help you. Some people use upstream and downstream in different ways.

    If I understand correctly, the flow detector is located on your cold water line after the junction that feeds your hot water system. Is that correct?

    It sounds like you do not believe that you have an actual leak (12 oz per minute would be fairly significant and unless it is below a slab, you would have likely seen damage by now.) However, you believe that there is mixing between the hot and cold water systems (cold water is being pulled into the hot water recirc system and hot water is being put into the cold water system.

    Do you have access to a main shut-off valve at the street or where water enters your house? One thing you can do is to shut off the water (take care - you may also need to shut off your hot water heating system to avoid a potential burn-out.) and then you can see if the system holds pressure. If you have a 12 oz/minute leak then a few minutes after you shut off your valve if you try any taps, the pressure should be completely out of the system and they won't give you anything. If you can turn off the main shut-off and then five or ten minutes later when you try a tap - if you get a quick burst of water (it was still pressurized,) then I'd be skeptical that you had an actual leak. That would help you confirm that the measurement is related to internal flows of water between hot and cold sides vs an actual leak into the ground, walls, toilet bowls, etc.

    I'd start by taking a close look at all of the visible plumbing. (You may need an IR temperature reader which can be bought for cheap or just run the system and feel the pipes.) All it would take is for the plumber to have mixed up one connection. Obviously the sink where you notice hot water coming out of the cold is a top suspect.

    Basically - you want to confirm that there is no connection between any of your cold water lines and your recirc system.

    Is it safe to assume that everything (don't forget things like washing machine and dishwasher and hose bibs) runs properly in a steady-state. Everything that should be hot is hot and everything that should be cold is cold?

    As a next step, I would consider the possibility of a faulty mixing valve. You will find those in every faucet that uses a single tap for hot and cold (e.g. most modern sinks and showers.)

    Keep us posted. Interested to hear what it was.

    The good news in all this is that you might save a bunch of energy. If you are accidently dumping cold water into a recirc line, that will not be as efficient.

  3. DrLou | | #4

    Thank you for your detailed response. I have added a schematic as you requested.
    The flow detector is located on the cold water line before, not after the junction that feeds the hot water system. And yes, everything runs properly in a steady-state. Everything that should be hot is hot and everything that should be cold is cold. And sincere thanks again!!!

    1. canada_deck | | #5

      Well that makes it a little more interesting... The water has to be going somewhere or you have a faulty sensor. You may also have an issue with your recirc system but best to look for the leak first.

      Next questions I would have:
      1) Have you tried turning off the main shut-off valve to the house? If you do, what does the meter show over the next 15 minutes if you don't turn on any taps? At the end of 15 minutes, is there still pressure in the system (as indicated earlier - you may also need to do something to your hot water heater to avoid a burn-out if you turn off the main water feed.)

      2) Do you have any in-slab plumbing?

      3) Isolate everything you can. As was already mentioned, you should have shut-offs for your toilets. Find any other shut-offs and turn them off as well. Does it still show water flow?

      4) Are you able to access the city water meter? With many of them, you will be able to see or hear if they are counting. It doesn't matter if you can tell how much they are counting - you just want to know if they are recording flow or not. If the FloLogic meter is telling you 12 oz/minute but the city meter is claiming zero then that's a good sign that your FloLogic meter is faulty.

      1. DrLou | | #9

        Many thanks again. We greatly appreciate all your valuable contributions. The answers to your questions are: 1.Turning off the main shut off gives us immediate 0 flow reading on FloLogic. At end of 15 minutes there is no remaining pressure in the system.; 2 We do have in slab plumbing with no evidence of a current leak. Prior owner of home (built in 2005) had an in slab leak repaired many years ago with no evidence of recurrence.;3. Even with all toilets and valves shut, we still show flow unless we shut the main valve just before entering foundation.; 4. I can access the city meter which always shows 0 flow when FloLogic is showing 15-20 oz/min. We have been in contact with FloLogic who have advised that their flow detection is much more sensitive than the city meter. They have explained that typically city meter only detects flow greater than 30 oz/min whereas FloLogic can detect 0.5 oz/ min.

  4. GBA Editor
    Martin Holladay | | #6

    Dr. Lou,
    This is a question unrelated to your actual problem: are you sure that the installer's decision to omit pipe insulation on your recirculation system complies with your local code? If you have a demand system, pipe insulation may not be required -- but if it isn't a demand system, pipe insulation is usually mandatory.

    See section N1103.5.4 of the 2018 IRC. (Of course, I don't know what code applies in your local jurisdiction.)

  5. Expert Member
    Akos | | #7

    Water filtration generally means an RO somewhere in the house. These tend to use a fair bit of water, each gallon of RO uses between 10 to 20 gallons of fresh water. I would check if the flow is not for your RO.

    You might also have some trap seal primers for the floor drains in the basement. If these are not running properly, they can also use a lot of water.

    Most likely culprit though is a toilet tank leak.

  6. DrLou | | #8

    Mr. Holladay: Again, many thanks for your time, insights and contributions! I appreciate your question re code compliance and I will get an answer!!!

  7. Expert Member


    If you've shut off the toilet valves, faucets, and water taps, and still see flow, you have a leak. It's unfortunate, but as simple as that. Confirmed by the 0 oz.min reading when you shut off the main. It's likely under the slab, because that's where the largest percentage of pipe runs, and otherwise you'd see wet walls at that leak rate.

    I'm not sure there's a leak big enough to show actual symptoms under a slab. Most slabs have the following layers - Dirt, 2-6" of gravel, plastic vapor barrier, and then concrete. The dirt under the slab has a lot of capacity, on top of that the gravel has a lot of capacity, and beyond that, the earth surrounding the house has a lot of capacity. You probably would never see signs of a wet floor due to the vapor barrier unless it happened in the same spot that was repaired, and they didn't replace it.

    Speaking from experience - I live in a house that is only 5 years old, slab on grade, with the construction described above. We had a sub-slab leak that was losing Olympic sized amounts of water that we saw no signs of (not even greener grass). It was as if it were running into the void. We had to cut drywall in several places to add shutoffs to finally isolate the span where the leak was.

    We didn't bust up the slab, instead we ran a line up through the wall, under the insulation in the attic, and down the wall to shower that was the end point of the line.

    While it's not common, I'm now a believer in the arterial design of water lines. One room with an easy to locate shutoff in each, be darned of the drawbacks.

  8. walta100 | | #11

    It seems you have eliminated all the above the slab possibilities and are left with the fact the leak is going to be difficult to find and repair.

    You need to decide if your local water is corrosive enough and if the pipes are old enough that they are at or near the end of your pipes useful life or if you think this leak is likely because of poor workmanship when the pipes were set in place years ago. The local plumbers should be able to tell you how long copper pipes will last with the local water.

    My in-laws house in phoenix it became necessary to abandon the sub slab water line as soon as you patched one pin hole leak another would open.

    If you decide to find and fix the leak rather than move the pipes above grade you will need a professional leak detection company the best ones do not do repairs only locate the faulty point with powerful microphones.


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