City water filling fresh water tank.

Tomf

Hi All, newbie here. We have our 2018 320 CS-S and loving it. Currently in Gulf Shores, AL heading to S FLA for the winter from Cape Cod, MA. Anyway… I noticed water coming out of the fresh water tank external fill last night ( we have been on and off city connections for 2 weeks now). I’m assuming it’s a stuck check valve but I’m not sure where that is or maybe that not the issue?  Any input would be appreciated. Thanks!

Gomers2

Disregard below! This is useful information but not for your problem. Sorry I didn't read your initial post carefully enough, I thought you were getting leakage from the city fill... 

Is that a nautilus system? If so the check valve is behind the little screen in the city water attachment. The manufacturer cautions against manually operating the check valve while the system is under pressure, which can lead to damaging the valve. I assume this means you need to turn off the pump and open the taps and possibly the fresh water tank drain before you mess with that valve. It's a little white button that you can push with your finger once the screen is off.

RVMike

I am not familiar with the T@B's check valve issue, but had plenty of experience with the issue is my previous RV. In that rig, the check valve was in the water pump.  One could buy the parts for $16, or just take the head of the pump apart, find nothing, and put it back together, and it works!  I am not saying this is the same as the T@Bs, it is a different system, different brand pump. 

In my previous rig, the symptoms were: 1) the fresh water tank would slowly over fill when hooked up to city water, 2) The water pump would come on for a fraction of a second every so often. My guess is that a little piece of crud got into the check valve.

Sometimes the problem would fix itself.  The immediate solution was to turn off the city water when not in use.

rfuss928

The check valve Gomers2 mentioned is to prevent backflow into the city water connection.  
Your description of a very similar problem in a previous RV is likely leading you to the cause in your T@B.  The pump used in T@Bs also has a check valve internally and could cause the leak into the fresh water tank you're experiencing. 

pthomas745

The check valve in the pump is probably stuck or failing.  There have been several threads on this in the past.

This one has a discussion, and a couple of other threads are linked. 

https://tab-rv.vanillacommunity.com/discussion/12636/check-intake-valve-for-city-water-sticking

There are some videos in those threads that might be old or no longer working.  There are other videos that describe how to remove the pump and fix or replace the valve.

And, this one, that explains a possible fix.

https://tab-rv.vanillacommunity.com/discussion/17852/water-coming-out-of-city-water-inlet-city-water-check-valve-stuck-open

Mickerly

I have the same trailer. The factory city water connection is plastic. Because of how it is molded, there is a ridge that cuts the seal. I replaced mine with the brass fitting made by Thetford. There are the same company that made the plastic one. I've had no issues for several years. The replacement is easy.

rfuss928

Mickerly said:

I have the same trailer. The factory city water connection is plastic. Because of how it is molded, there is a ridge that cuts the seal. I replaced mine with the brass fitting made by Thetford. There are the same company that made the plastic one. I've had no issues for several years. The replacement is easy.

The check valve causing the problem in the OP is internal to the pump.  When working properly it prevents system pressure from causing flow back to the fresh water tank when the pump stops.
The check valve in the city water connection prevents flow exiting from the connection when the pump is pressurizing the system.  When it fails, system pressure will result in water flowing out of the connection into the Nautilus box.  It is also required to prevent "possibly contaminated" backflow into the "city" supply line.  It's good to know there is a more robust inlet connection part available if needed.