Freshwater tank won?t quit filling!

[donandlin]

Our 2014 Holiday Rambler Ambassador is in a park with full hook ups. We are hooked up to city water  but the water is filling our freshwater tank even though the valve says city water, not tank fill. We have turned off the city water and are using the pump with water from the tank. Any suggestions on where to start  looking to determine the problem? Thanks.

 

[RVfixer]

You could have a cross leak (bad o'ring) in the water selector valve.  I don't have that selector valve in my trailer so I don't know how to tell you how to troubleshoot that except to take it apart and see what you find.  First, I would check the water pump.  When you put city water pressure on the system it puts pressure on the water pump outlet side.  The pump has a check valve inside that prevents the city water from leaking back into the freshwater tank. Remove the line from the pump to the tank from the inlet side of the pump to see if water is leaking back.  If it is you can buy a "no-Back" check valve from Home Depot or the like and install it on the inlet side of the water pump.

 

[Henry J Fate]

Two ways the water can leak into the tank while connected to city water. Both of these failures can be reduced or eliminated with a good pressure regulator on the city water connection. If you are not using one, you should install one. If you are using one, be sure it is keeping the water pressure at the designed level.

The selection valve could be leaking or the pump back flow protection valve could be passing city water to the tank.
Checking both of those can be done fairly easily but should be done once a regulator is in place and functioning properly.

 

[Rene T]

Remove the line from the pump to the tank from the inlet side of the pump to see if water is leaking back. 

Make sure you do this with the tank empty.

 

[RVfixer]

Rene T...The tank would not have to be empty, just down a little so there is no pressure from overfilling from the city water leak back.  When you break the line from the pump inlet the water in the line would drop to the level in the tank.  You could not even start a siphon action by sucking on the line unless you lowered the end of the line to a level below the level of the water in the tank.

 

[Rene T]

Rene T...The tank would not have to be empty, just down a little so there is no pressure from overfilling from the city water leak back.  When you break the line from the pump inlet the water in the line would drop to the level in the tank.  You could not even start a siphon action by sucking on the line unless you lowered the end of the line to a level below the level of the water in the tank.

Many tanks are mounted under a bed and the pump is right next to the tank. If the tank is full of water and you disconnect the inlet line at the pump, you're going to get a tankful of water in the bedroom.
The OP was told by you that a way  to check the check valve in the pump, it could be done by disconnecting the line going to the tank and seeing if water flows through the pump when under city water pressure.  Which is true but the tank some tanks must be emptied prior to doing this.

 

[donandlin]

We?ll start checking, thanks. We do use a good regulator.

 

[Gary RV_Wizard]

Two simple causes are possible:

1. The city fill valve is leaking, allow water to move from the pressurized side to the tank via the water pump bypass tube.  Typically that  valve is just a simply inline shut-off valve and ought to be redily available wherever water valves are sold.

2. The water pump has failed internally and water is passing through the pump in reverse, into the tank. Since you are able topump water from the tank, this problem seems unlikely.

I sincerely doubt a regulator of any type will help. Any water pressure at all on the pressure side (city & pump) is going to cause water to flow to the tank.

 

[RVfixer]

Rene T  Yeah, that makes sense I didn't think of that because I have never had or have seen an installation were the tank wasn't well above the pump.