If your RV freshwater tank is filling up while you’re connected to city water, you may have a problem with the water pump’s internal check valve.

In this 5-minute troubleshooting video, I’ll show you how I diagnose this problem and explain why the freshwater tank can slowly fill even though you’re using city water. The water pump has a check valve that is supposed to prevent city-water pressure from flowing backward into the freshwater tank, but when that check valve fails, it can allow the tank to fill.

If you’re finding water in your freshwater tank while hooked up to city water, this is one of the first things I would check.