When camping or RVing my wife and I typically pump water from our fresh water tank, even when we have a city water connection. We prefer it because the water pressure for showering is better. But on our last excursion, I decided to run a city water connection. Before we left I emptied the fresh water tank completely. However, after camping for a day or so I happened past the panel that shows our holding tank levels and noticed my fresh water tank was two-thirds full!! Suspecting a bad sensor I went out and opened the valve for a few seconds, and sure enough, fresh water came gushing out. So, at SOME point water got into the fresh water tank from the city water connection. I'm curious if anyone has had this happen and if you have any information on how to solve it.

Ours is doing that right now. Filled both 40 gal fresh water tanks and is dripping out of both overflow tubes. Wife turned the pump on as I was hooking up city water outside. Don't know if we messed up a backflow valve or something.

Might be a leaky check valve on the pump or a leaky shut off valve depending on how your camper is plumbed.

The most common cause is the pump check valve has probably clogged with debris so it can't properly seal, allowing city water to back flow through the pump and into the fresh water holding tank.

my bounder had a small valve to stop flow to tank that had a small O ring that had a tiny crack in it and it would let incoming water go into the tank.bumpy

How do you normally fill fresh water tank?Gravity fill port or a 'valve/switch' you turn to FILLGravity port...then pump internal check valve is not closing and allowing backflow thru pump when using city water. Typically you run pump/flow water thru pump and clear the debris etc BUT you use pump frequently so probably need to replace internal check valve in pump'Fill' valve/switch...Leaking thru/bad o-ring --bad valveOR pump internal check valve

Water seeping from city connection to fresh water tank

lostbytes
Explorer
Aug 25, 2018
Well. My question is a little more. What is the pump seal/check valve pressure vs city water pressure? The city is higher normally. Could be that the check valve (pump) is suspect. Put a one way valve in the line to help? Especially if pump is fairly new... Just another way to look at it.
Me_Again
Explorer III
Aug 24, 2018
Old-Biscuit wrote:
How do you normally fill fresh water tank?
Gravity fill port or a 'valve/switch' you turn to FILL

Gravity port...then pump internal check valve is not closing and allowing backflow thru pump when using city water. Typically you run pump/flow water thru pump and clear the debris etc BUT you use pump frequently so probably need to replace internal check valve in pump

'Fill' valve/switch...
Leaking thru/bad o-ring --bad valve
OR pump internal check valve

Anderson valves a noted to have O-ring issues if switched between settings with pressure applied to the water system. The core is easy to change with you get a replacement.

Chris
Hannibal
Explorer
Aug 22, 2018
I shut off the city water, bled off the pressure and then ran water from the pump/fresh water tanks through the sinks for about 20 minutes last night. Then shut the pump switch off and turned the city water back on. No more back feed to the fresh water tanks. Must have been some debris in the check valve.
Clarryhill
Explorer
Aug 21, 2018
As others have already said, probably faulty check valve in the water pump. Just had that happen to us this spring.
LeBout
Explorer
Aug 21, 2018
I appreciate all the responses to this thread. Thanks for the insights and help!!
Lwiddis
Explorer II
Aug 21, 2018
A another example of why I only use city water to gravity fill my fresh water tank and use the pump.
Old-Biscuit
Explorer III
Aug 21, 2018
How do you normally fill fresh water tank?
Gravity fill port or a 'valve/switch' you turn to FILL

Gravity port...then pump internal check valve is not closing and allowing backflow thru pump when using city water. Typically you run pump/flow water thru pump and clear the debris etc BUT you use pump frequently so probably need to replace internal check valve in pump

'Fill' valve/switch...
Leaking thru/bad o-ring --bad valve
OR pump internal check valve
Bumpyroad
Explorer
Aug 21, 2018
my bounder had a small valve to stop flow to tank that had a small O ring that had a tiny crack in it and it would let incoming water go into the tank.
bumpy
SoundGuy
Explorer
Aug 21, 2018
The most common cause is the pump check valve has probably clogged with debris so it can't properly seal, allowing city water to back flow through the pump and into the fresh water holding tank.
GrandpaKip
Explorer II
Aug 21, 2018
Might be a leaky check valve on the pump or a leaky shut off valve depending on how your camper is plumbed.