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Old 02-06-2024, 11:40 AM   #1
1 Rivet Member
2017 30' International
Los Angeles , California
Join Date: Feb 2023
Posts: 5
Fresh Water Tank Mysteriously Refilling Post-Sanitation

Yesterday I completed my first routine sanitization of the fresh water system in my "fairly new-to-me" '17 International Serenity 30RB. The whole process went splendidly, or so I thought until I woke up this morning to find the street-side fresh water tank input leaking water everywhere and the ground very wet. Mysterious! I'm hoping I just missed a step. Here are the details.

To start, I haven't yet had the occasion to actually use the fresh water tank. Since I bought the AS, the tank monitor has read a steady 15% for fresh water. The water pump works, but I leave it off since I use city water daily from a spigot.

I followed the fresh water sanitization process, and to end, I refilled the fresh water tank back to 15% with filtered water, turned off the water pump, reattached the spigot to the curb-side water input, turned the spigot on, cleared the system, and went to bed. At that point, the monitor read 15% for the fresh water tank, and both the gray-water tank and black water tanks were zero, since also I dumped them yesterday.

When I woke up this morning to find water all over the ground and water (gently, at that point) gushing out of the street-side fresh-water input, I went inside and checked the monitor. The water pump was off, how I left it. But the monitor read 100% for the fresh water tank. (And, oddly, the black-water tank was also higher than I left it the previous night). How could that be? I wondered, is there any way for fresh water to get in the fresh water tank without me putting it there? I have been using city water from the spigot for the last six months without issue; this is the first time anything like this has occurred. Wait, there's more.

I turned off the spigot. I dumped the fresh water tank, as I had done twice the day before as part of the sanitization process. After that, again, the monitor read 0% for all three tanks. I did not put any water back in the fresh-water tank. The water pump was off. I then turned on the spigot connected to the curb-side input and cleared the lines briefly using the kitchen faucet. Here we go.

With NO water running, and me just sitting here, I watched the reading on the fresh-water monitor start to creep up. The fresh water tank suddenly read 5% in about 5 minutes, then 10%, then 15%. I noticed the black-water tank read 6%. I turned the spigot off. What in the world?! I promise: I put nothing in the fresh water tank using the street side water input.

Thank you for sharing your thoughts and advice. Much appreciated!
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Old 02-06-2024, 12:50 PM   #2
Rivet Master
2019 30' International
Pennsylvania , Pennsylvania
Join Date: May 2016
Posts: 1,229
Your on board water pump has a backflow preventer in it. That has either failed, or is stuck open.

Turn off or disconnect the city water, and run the pump for a spell, maybe an hour, maybe a day or two.

Then turn the pump off, and reconnect the city water, and watch the freshwater tank reading to see what happens.

This is actually not uncommon, and several threads on here discuss the issue.
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Old 02-06-2024, 02:05 PM   #3
1 Rivet Member
2017 30' International
Los Angeles , California
Join Date: Feb 2023
Posts: 5
@majorairhead. Thanks for the response. I've turned off the city water, turned on the water pump, and will recheck later. Meanwhile, I'll search for the other threads you mentioned. Thanks again. Fingers crossed.
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Old 02-07-2024, 06:55 AM   #4
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2008 27' International FB
Petaluma , California
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Here's a good search link for google: water filling on its own
Looking for adventure in whatever comes our way.

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Old 02-07-2024, 08:23 AM   #5
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2017 26' Flying Cloud
Tampa , Florida
Join Date: Feb 2017
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None of the usual tricks to unclog the back flow valve worked.
I replaced the pump with a new unit.
I always wanted a spare anyway, right?
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Old 02-07-2024, 11:04 AM   #6
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2017 30' Classic
2022 Interstate 24X
Carlisle , Pennsylvania
Join Date: May 2017
Posts: 15,647
Originally Posted by Mollysdad View Post
None of the usual tricks to unclog the back flow valve worked.
I replaced the pump with a new unit.
I always wanted a spare anyway, right?

Indeed, pumps are pretty cheap / easy to get. Installing a new one is a bit fun, but it's just bashing your knuckles here and there. It should be a DIY compatible project.

While you are at it, take a look and see if you have a winterize / anti-freeze feed setup on the input to the pump. If not, it's a fine time to install one.

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Old 02-08-2024, 08:02 AM   #7
3 Rivet Member
2017 25' Flying Cloud
Woodway , Texas
Join Date: Oct 2017
Posts: 151
Shurflo Pump Problems

Our Shurflo pump also started dumping water into the fresh water tank when hooked up to city water. Since you've kept your old one as a backup, you might go ahead and replace the check valve which will solve this problem. Kits run about $12 - $23 and it's about a 15-minute job once you have the pump out of your AS.
The instruction sheet covers all parts of your pump as well so it's a good source for any disassembly you might want to do in the future.
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Old 02-12-2024, 07:09 AM   #8
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2017 27' Flying Cloud
Boulder , CO
Join Date: Jan 2024
Posts: 10
I put in a new kit to try to solve this problem and then replaced the whole pump but neither one fixed the problem. Ended up putting in a ball valve in the line from the pump to the freshwater tank (easy mod if you have the tools). I have to remember to open it up when we are boondocking but it is a very definitive way to solve this problem.
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