Fresh water tank filling up

[ntrainman]

Trying to figure why and how the fresh water tank is filling up when we hook up to the city source. This is on a Class C Conquest motorhome. I drain the tank before we leave and close the valves when we arrive. We are not filling the tank from the tank inlet.

[atreis]

There's a check valve at the city water connection that is meant to prevent back-flow to the tank. They sometimes stop working properly and let water through. It needs to be replaced.

[ntrainman]

Now that we are home I'll take a look. Thanx.