Fresh water tank filling when hooked to city water

I just bought a cyclone 2014 3100 that is only been used 6 times from the previous owner. So our second trip out we got a water leak under the trailer. Long story short it was the main hose from one fresh tank to the second , so I pulled the hose off to check it out and both tank were completely full, and should have been empty. Both tank got full from city water connection, is there a check valve that was hung up or something causing this issue, any info would be great

There is a check valve as part of the water pump. At times they can become tired.
If your Cyclone has the Anderson water valve, water can also leak past the O-rings.

Peace
Dave

We just had the same issue.... was anderson four way was bad, I call number posted else were , and the nice fellow sent new one free....., changed it out our selves, not to bad, make sure you get snap washer in right postion, or its hard to get that brass fitting back on...

Most commonly caused by the internal check valve in the water pump getting stuck partially open. The easiest fix is to get a $15 Sharkbite 1/2" pex check valve and put it on the suction/input side of the pump.

CDS3100, are you familiar with how the Anderson valve works? You did not say where it was set at.

I have been tracking down this issue a little at a time for a few months now. I to was thinking it was the Anderson Valve, Heartland sent me a new valve after it arrived I did some bench testing to learn how it works. After figuring out how it works I removed the 2 lines on the back of the Anderson valve 1- the fresh water line and 2- the water pump suction line, I stuck the water pump suction line in a bucket and turned on the city water---- waited and watched nothing whatsoever came out of the fresh water tank port. (It's not the Anderson valve) At first I did get some water out of pump suction hose meaning it's the the pump check valve. Heartland sent me a new pump and I haven't installed it yet.
Here's a link
https://heartlandowners.org/showthread.php/54076-Project-LM-365?p=479218&viewfull=1#post479218

I also had the same problem with the Anderson Valve filling the Fresh Water Tank in the City Water position. I emailed Anderson explained the problem and they sent me a new repair kit (cartridge) free! I installed it and has been working fine. Under test for a week now, no leaks! I experienced the same install issues as RETIREDDK getting the snap washer in the correct position.