City water fills fresh water tank

[GRUBBS]

I am sure IF the water had gotten to the top it would have ran out at vent, but what actually happened was the water filled enough to fill the tank to the level it increased the pressure on the lines near where the water pump is mounted. On the line adjacent to the pump there is a dead end tube (it's where you can install a piece of tubing so when I winterize, I take the plug out, put the end in a gallon of pink RV antifreeze solution, which protects me from getting into my Fresh water tank, turn the pump on a it will circulate the antifreeze...The plug on this tubing had never been properly tightened.
All is good now, THOR replaced the water pump. They explained to me that something even as small as a hair would cause this check valve to not properly seal close and because I do not use the Fresh Water tank, when it slowly filled the tank, the water found it's easiest route and flowed out under the bed. There are probably a million items on a New Coach to check, this is one! I appreciate all the thoughts and advice!

[BigSkyBob]

A very easy fix for this issue is to install a shark bite check valve in the line feeding the fresh water pump. My pump has 5 check valves to prevent back flow but water still seeped into the fresh water tank. I cut the PEX tubing and installed the shark bite check valve in 5 minutes, issue resolved. A whole lot less work than replacing the pump and is pretty much bullet proof.