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  1. #1
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    Fresh water tank/pump issue

    2017 Momentum 350M

    When dry camping I'm experiencing issues with air getting into the pump if it sits inactive for a couple hours. If you run the pump for a long period, it clears the air from the lines and if you use it often all is fine but if I don't run the pump often, like going to bed, somehow air is getting in the tank-to-pump run (water draining back to the fresh water tank). So at this point if you run water for a short period , like a middle of the night toilet flush, it will pump the water that was in the pump-out side and flush the toilet but the pump now draws the air that got into the pump inlet line into the pump. At this point, the toilet flush is complete but now air is in the pump with no place to go so the pump will run forever.
    I put in a new Shurflo 4008 pump, new strainer, and added an accumulator, with the same results. I looked at the Nautilus P1 (wow, what a Rube Goldberg design!) and checked the valve behind the black handle. All seems OK but with that octopus orgy of PEX tubing it's difficult to tell.
    I called Grand Design tech support and after holding forever I finally talked to someone who said it was the City Water Inlet check valve. Ummmm OK, that valve won't prevent anything from "coming in" then when transferred to parts all communications ended. I thought about adding a inline check valve to the tank to pump line so water can't drain back to the tank but am not sure of the implications .
    Any help appreciated, my next move is replace the Nautilus P1 or have the line running into the tank check for holes.

    Thanks in advance
    Scott & Deb
    2017 Momentum 350M toy hauler fully loaded with full paint job.
    2017 Ford F450 Lariat

  2. #2
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    Ill bet that the soft pex line between the pump and the fresh water tank has collapsed or has a kink that comes and goes. Can you duplicate your issue while watching that line?
    Good luck
    2018 Reflection 150 Series 220RK 5th wheel with 6K axle upgrade. B&W 25K OEM Companion, Steadyfast system, 2022 F350 SRW 6.7 King Ranch 8' bed, Trailer reverse lights, rear spare tire holder, storage tube, sumo springs, Victron MultiPlus 12/120/3000, and Solar

  3. #3
    Rolling Along
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    Have you adjusted the pressure sensitivity switch? Depending on pump it's a tiny alen head screw at the front of the pump. It's a very fine adjustment. A little off and your pump won't shut off properly. A little off the other way and the pump sputters.

    I readjusted mine and the pump works much better now.
    Charles and Susan
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  4. #4
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    I have not adjusted the sensitivity switch, I'll check it out. But all works well when the lines have water, the air in the pump is the problem. It can't build pressure to shut off (since the taps are closed the air has nowhere to go).
    Scott & Deb
    2017 Momentum 350M toy hauler fully loaded with full paint job.
    2017 Ford F450 Lariat

  5. #5
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    I see no kinks or pex irregularities but then again I can't see what's going on "below deck" to the tank. I have know idea how that tube draws from the FW tank, is there some take up connection built in the tank or does that PEX tube just go in the tank. Watching the line would be like watching paint dry, it takes hours for this "air penetration" to happen and that passthru isn't the most comfortable place to be. I think you are on the right track in your thinking also, it's like water in a raised straw. It will stay there as long as there's no air penetration. I think this is what this design depends upon but mine has an air leak.
    Scott & Deb
    2017 Momentum 350M toy hauler fully loaded with full paint job.
    2017 Ford F450 Lariat

  6. #6
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    Quote Originally Posted by scoganz View Post
    I see no kinks or pex irregularities but then again I can't see what's going on "below deck" to the tank. I have know idea how that tube draws from the FW tank, is there some take up connection built in the tank or does that PEX tube just go in the tank. Watching the line would be like watching paint dry, it takes hours for this "air penetration" to happen and that passthru isn't the most comfortable place to be. I think you are on the right track in your thinking also, it's like water in a raised straw. It will stay there as long as there's no air penetration. I think this is what this design depends upon but mine has an air leak.
    There is a spun weld fitting on the side of the tank near the bottom. It is very close to the fresh water dump valve, so dropping the coroplast in that spot might give you a look. On my tank its located in a depressed area that the dump valve is bolted to.
    2018 Reflection 150 Series 220RK 5th wheel with 6K axle upgrade. B&W 25K OEM Companion, Steadyfast system, 2022 F350 SRW 6.7 King Ranch 8' bed, Trailer reverse lights, rear spare tire holder, storage tube, sumo springs, Victron MultiPlus 12/120/3000, and Solar

  7. #7
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    Thanks for that valuable info! I wish there was a Chilton or Haynes type repair manual for these units.
    Scott & Deb
    2017 Momentum 350M toy hauler fully loaded with full paint job.
    2017 Ford F450 Lariat

  8. #8
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    Just a quick finish, the issue was a small leak of a seal inside the Nautilus "valve" to fresh water tank. If you remove an elbow from the valve assembly on the Nautilus there is an internal double-ended seal, this leaked apparently. I couldn't find them for sale anywhere, after many calls a technician sent me a hand full for free (the manufacturer of the plastic fittings). This small leaked allowed air to leak back into the line as the water drained from the line back into the tank. If a quick water request was done (quick toilet flush) this pulled the air from the line into the pump and without a faucet open the pump would run and run because the air had no where to go.
    Scott & Deb
    2017 Momentum 350M toy hauler fully loaded with full paint job.
    2017 Ford F450 Lariat

  9. #9
    Site Sponsor Crazybanshee's Avatar
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    scoganz I am having the same issue. Can I get the fitting manufacture info so I can get some of the seals. If I have to buy the whole fitting I will do that. Thanks
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  10. #10
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    I contacted "B and B Molders" (www.bandbmolders.com). Their website will tell you to go to RVLOCKSandmore.com. I didn't see the parts at RVLOCKSANDMORE so I called B and B. I got a hold of someone who said they had those parts all over the place and would send me a handful of various pieces, which he did!! No cost. Elbows, tees, and those "never seen anywhere" internal seals. So I replaced the seal (the old seal end was kinda smashed) and the elbow since I had it apart. Problem over!
    Before the fix I had to turn my pump off at night in case I woke up to take care of business. I didn't like standing there listening for the pump to shutoff, especially if the AC was on because its really hard to hear. That short flush was enough to allow air into the pump from the takeup line then the air had no where to go so the pump would run and run because it couldn't build pressure.
    Scott & Deb
    2017 Momentum 350M toy hauler fully loaded with full paint job.
    2017 Ford F450 Lariat

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