Fresh water tank mysteriously filled while plumbed to city water fill???

[CL1981]

Here’s a weird one for you:

We’ve been parked at the same location for 2 weeks now. The water hose is hooked to the “City Water Fill” input.

Tonight I could hear running water outside and I found that my fresh water tank was overflowing. I checked and sure enough my fresh water tank is randomly full which is weird because I have no water going in to the “Fresh Water Tank Fill” input.

I’m not familiar with the inner workings of our rigs plumbing but How is this possible?

[bduemig]

Water pumps have an internal check valve. When they leak, they can fill the n fresh water tank

[hclarkx]

BD nailed it. After having this problem and too high of city water pressure and a failed pressure reducer and a frozen hose, I gave up on city water. I now simply fill the fresh tank from the city water and use the pump. This does mean keeping an eye on the fresh tank level, of course, especially if the DW is about to take a shower.

[CL1981]

Interesting so you’re saying we have a leak in the water pump? we just had a brand new water pump installed less than a month ago

[rarebear.nm]

Does your city water connection inlet have a three-way valve that allows you to fill the tank while on city water? This is fairly common feature. If so these valves can set at some intermediate position that would allow filling the tank while getting normal water flow inside from the city water connection.


Some RVs have an remote controlled electronic valve (solenoid valve) to provide this feature opposed to a three-way valve. Our 5th wheeler has a solenoid valve while the MH has a three-way valve. Same result just different operation.



I agree with above post in cold weather to just fill the water tank and use the pump for water needs. Remove the water hose at both ends and drain it so you use it again after freezing weather.


It would be unusual for a new pump to fail with a blow check valve. But failures occur according to a bell shaped curve and a very premature failure is possible. Reason for warranties.

[dssl]

Originally Posted by CL1981

Interesting so you’re saying we have a leak in the water pump? we just had a brand new water pump installed less than a month ago

The water pump check valve is by far the most common cause. It can also be a bad fresh water fill valve which in many coaches can be a PITA to replace.

Disconnect the inlet to the pump(which is something you do to winterize) and turn on the city water. If water comes out the Inlet then you know that it's a check valve problem.

[lazybyrd]

Even though the pump is new a tiny piece of debris (pipe plastic, thread sealant, etc) is all it takes to hold the check valve open.
I had the same problem with my tank filling while on city water. Turns out my three way valve was bypassing to the tank.

[GypsyR]

My coach has a valve where I can turn it to fill the tank or just supply water. I've seen others that have the same valve AND a separate fill port for the water tank. Mine had seal issue with the valve and filled my tank overnight once.
But since someone has recently been working on the pump I'm with the others and that would be the first place I'd look.

[CL1981]

Awesome thanks for the advice everyone!

[hamm2018]

On our 5th wheel, the Anderson Valve was leaking by allowing the fresh tank to fill. If you have an Aderson Valve it could be leaking by.
If you have an Anderson Valve, turn your water off, relieve the pressure, rotate the Anderson Valve slowly a couple of times, it may stop the leaking by.

It worked on our Anderson Valve for a couple of months, then it needed replaced.

https://www.abcorv.com/

[Old-Biscuit]

How do you fill your fresh water tank?
'Fill' Valve/Switch using City Water Connection
OR
Gravity Fill Port


Fill Valve.....could be source of leak filing fresh water tank
Pump Internal check valve (diaphragm) not fully closing so city water is backflowing thru pump filling fresh water tank

Use the pump ---run water thru it....can help clear the diaphragm
**W/O city water connected and pump on but no demand (faucets off etc) and then you hear pump short cycle every once in a while...Pump Check Valve is not closing off

[HighDesert]

Originally Posted by bduemig

Water pumps have an internal check valve. When they leak, they can fill the n fresh water tank

Depending on the make of RV you have, you may well also have a check valve in your city water connection that is stuck open. Been there and done that. Often, you can reset the valve by inserting a small, stiff rod and press the check valve.

[153stars]

Change valve to pump.Run off the pump with few faucets open for max flow and then use tank up. Fill fresh tank a bit with hose again on purpose. If it's small bit of debris in a check valve, it may wash out or reseat ....worth a shot anyway.
Also if check on pump is leaking back ,it will cycle and zero you in. Keep hose disconnected and we if water come out of hose connection from pump.

[Old-Biscuit]

Originally Posted by HighDesert

Depending on the make of RV you have, you may well also have a check valve in your city water connection that is stuck open. Been there and done that. Often, you can reset the valve by inserting a small, stiff rod and press the check valve.

All city water connections have internal check valve
They prevent backflow from RV System into City Water System
*Stop backflow when using pump