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Freshwater overflow won’t stop

benpcbenpc Member Posts: 17
in Heating/Plumbing & Winterizing

Hi all, first time owner here, sanitizing and filling my 2024 400 BD tanks for our first season. I’m running into an issue where the freshwater overflow valve starts dumping water… and won’t stop!

The basic pattern is this:

  • Empty hot and cold lines with low point drains
  • Set Nautilus to power fill, and start filling fresh water tank. I can feel air coming out of the what I think is the freshwater overflow valve (driver side, underside of the Tab between the tire and the Nautilus) as the tank fills up. 
  • After 17.5 gallons or so (as measured on an inline water meter, which, to be fair, I have not calibrated) the valve starts dumping water. I believe my tank should be 28 gallons or so. Convenience panel only reads 2/3 full. 
  • Aaaand it keeps dumping water! Opening / closing faucets makes no difference, nor does removing the city water screen and pressing the check valve; does not seem to be an airlock thing. 

The most recent time I let it go for 12 minutes before I got bored and flipped over to dry camp mode. Changing the mode on the Nautilus didn’t do anything, but 15 seconds after I started the water pump to fill and pressurize the plumbing, the overflow drain stopped leaking. 

Camper lives offsite so I’m looking to get a list of things to try the next time I’m over there.

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Comments

  • benpcbenpc Member Posts: 17
    I’ll add that once it stopped draining, everything seemed to work normally. All faucets get good pressure on both hot and cold sides. This unit has an Alde flow FWIW. 
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  • pthomas745pthomas745 Administrator, Moderator Posts: 4,521
    The gauges for the various tank levels are "estimates" at best, and plain wrong at worst.  If your fresh water "vent overflow" has water coming from it, that means it is full, or close to it, and will be a better signal than any of the tank monitors.
    One thing to be careful of when filling the tanks with this over flow setup is the possibility that the "vent overflow" has been clogged by either water loving insects or what have you.  There have been a couple of incidents in the past where the clogged vent prevented air from escaping as water filled the tank, and the tank and surrounding supports were damaged.
    Your trick of sensing the air escaping the vent while you tried to fill the tank is a good one.There have been some design changes in that little "spout" under the trailer...I believe your 2024 is a simple blue downspout?  Newer trailers have some sort of "ell" fitting down there.

    2017 Outback
    Towed by 2014 Touareg TDi
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  • benpcbenpc Member Posts: 17
    Yep that's right, it's a little L fitting behind the wheel. And I am certainly taking the convenience panel with a grain of salt, same with the in-line hose gauge (at least, until I calibrate it!).

    What's puzzling me is that it's not like a *little* water comes out and then the water level settles below the overflow... gallons and gallons and gallons come out without stopping! I do not understand the physics involved here! 

    Poking around the forum; could this be a famous yellow flapper situation? I haven't checked that yet.
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  • pthomas745pthomas745 Administrator, Moderator Posts: 4,521
    The "Famous Yellow Flapper Valve" spout is a clear plastic sort of thing.  You should have two of them in your 400.

    If the water was coming from the "L" fitting, that is the vent overflow for the fresh water tank.
    This thread shows the issue I mentioned about a clogged vent/overflow.  It shows a photo of how the overflow is routed from the top of the tank to where the actual drain is.
    This trailer was a 2021, so I'm guessing there may have been some design changes, but have a look.
    Here is a picture of where the Yellow valves are in your trailer.  If the water stopped draining after you started pumping water, it "probably" isn't
    a yellow valve issue.  Note: the valves in this photo are Open, and they should be horizontal to be closed. 

       
    2017 Outback
    Towed by 2014 Touareg TDi
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  • BridgerSunsetBridgerSunset Member Posts: 109
    I've had some success in stopping the overflow by simply blocking flow with your thumb for a bit of time.  I suspect, but don't really know, that this action interrupts what appears to be a "siphon" effect.  This siphoning starts a vacuum flow that continues until pressures/water levels equalize.  

    Kinda like gas thieves stealing from a gas tank by a siphon hose, I suppose....
    2021 T@B 400 Boondock  - Chev Silverado 2500HD 6.6L
    Montana USA


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  • benpcbenpc Member Posts: 17
    @BridgerSunset I think you're on to something. It hit me last night that my storage spot isn't level, in fact, the Nautilus / overflow size is on the downslope. Could contribute to starting a siphon (and trapping an air pocket) before the tank gets fully filled. 🤔

    Next time I'm able, I'll properly level the trailer, try again, and report back!
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