2007 OKanagan 117

Hello and good evening Bosun

Truck Campers usually have 3 check valves in the water system.

1: City Water Fill
You cannot see it but its there to stop water from coming out of that device when you are using on board water. Your water pump is drawing off your fresh water tank and pressurizing your entire R/V. That Check Valve stops the water from leaking out that city water fill

2: Water heater (Discharge side-hot water coming out of the tank)
It looks like a 2" plastic nipple coming out of the hot water side of your water tank. Its internals consists of a spring and plastic ball.Its put there to stop the back flow of anti/freeze when you are winterizing and putting in that pink stuff. If it was not there, you would be pumping 5 gallons of anti-freeze inside your water heater.

Now saying that there are some MFG who opted for basic shut off valves and you maybe not have a check valve!!
But based on your comment of the lack of water pressure, my vote is yes you do have a check valve

3: 12 volt Water Pump
Its part of the water pump assembly to stop water from back filling into your fresh water tank

A) You have a bad check valve in your water pump - Replace the entire unit
b) You have calcium build up in that check valve on the discharge side (Hot) of your water heater. Replace with a brass check valve

I know you said it's filling your tank with city water fill, with that said, there is usually a check valve on the water heater outlet side. mine was on the heater unit itself. If that check valve is letting water through it will fill the water heater tank as well as the fresh water tank. Mine went bad and did exactly what you are describing. If the water pump has seen a better day I would replace that as well. Both parts are dirt cheap and easy to replace. Easy check by taking out your water heater plug and see if water flows out as you turn on the city water. That should fix it. The pervious owner might also have put in a diverter valve.
Good luck, Joe

PS This is all assuming you have the water system on normal and not winterize. There are three winterizing valves in my 1181.

Yes. The water shouldn't be going back through the pump. Could be something holding the pump valves open or the pump may be bad.