I have been at a campsite in Charleston since Saturday. I noticed yesterday afternoon that my fresh water tank said it was full. I wrote it off to being a typical RV tank gauge being stupid (the day before it read 1/3 tank and I have been hooked up to city water since Saturday). Went out today to eat lunch and when we got back to the trailer, my wife asked why there was water on the ground next to the trailer. Below the fresh water tank fill was a puddle of water. In opened the cap and I could see the tank was full??? I turned off the city water and turned on the water pump. Figured it was time to flush the black tank. Used enough water from the fresh water tank to fill up the black tank. This used enough water to make the fresh water tank read 2/3 tank. Turned off water pump and went outside and turned on city water. Checked a few hours later and fresh tank is full again???? Anyone know what is causing this? Is there some type of valve that could be leaking that if back filling the fresh water tank?We only have two nights left on this trip so I guess I will just use the fresh water tank and pump until we get home. I don't want to damage anything more by turning on the city water.Burch

Two ways water can get to fresh water tank while hooked up to city water1) If you have valves/switches on a water panel the 'fill' valve could be leaking thru 2) Internal check valve of on-board pump is leaking back thru pump to tank***If you have gravity fill forget #1. It's the pump check valve leaking.You can disassemble pump and try to flush any debris, replace the internal check valve or install an in-line check valve in suction line to pump.Sometimes just running pump will clear and debris holding check valve open.Use it the rest of your trip and then test next trip/at home.

Do you have a manual valve at or near the city water connection where you can direct water to the fresh water tank? Maybe it isn't fully switch to the correct position. Or id there a check valve not working properly?

One of your check valves is leaking. (the one that is on the storage tank side of the system) If your RV is piped like the others that I have seen, that check valve is allowing the city water pressure to back feed into your potable water tank. Most RVs will have two check valves. One to stop water from back feeding into the potable water tank and the other to stop the RV water pump from back feeding into the city water system.

If you have gravity fill... DO NOT forget #1. unless that is the ONLY way to fill your tank,, MOST Rv's have Gravity fill (though sometimes finding it can be a job) Many also have some kind of "Quick fill" like mine I have both.

Old-Biscuit wrote:***If you have gravity fill forget #1. It's the pump check valve leaking. I do have a gravity fill. I guess I am lucky that the water was oozing out the small vent hole of the fresh water tank. Glad I didn't come back to water inside the trailer. I usually turn off the water when I leave my site but I don't always remember.I will be driving about 250 miles tomorrow to get halfway home. I will use the pump until tomorrow morning and then maybe try city water again when I get to the next stop. Maybe whatever debris is causing the issue will vibrate loose on the drive.

Fresh water tank filled itself | Good Sam Community

MetalGator
Nomad
May 29, 2014
Old-Biscuit wrote:

***If you have gravity fill forget #1. It's the pump check valve leaking.

I do have a gravity fill. I guess I am lucky that the water was oozing out the small vent hole of the fresh water tank. Glad I didn't come back to water inside the trailer. I usually turn off the water when I leave my site but I don't always remember.

I will be driving about 250 miles tomorrow to get halfway home. I will use the pump until tomorrow morning and then maybe try city water again when I get to the next stop. Maybe whatever debris is causing the issue will vibrate loose on the drive.
wa8yxm
Explorer III
May 29, 2014
If you have gravity fill... DO NOT forget #1. unless that is the ONLY way to fill your tank,, MOST Rv's have Gravity fill (though sometimes finding it can be a job) Many also have some kind of "Quick fill" like mine I have both.
69_Avion
Explorer
May 29, 2014
One of your check valves is leaking. (the one that is on the storage tank side of the system) If your RV is piped like the others that I have seen, that check valve is allowing the city water pressure to back feed into your potable water tank.
Most RVs will have two check valves. One to stop water from back feeding into the potable water tank and the other to stop the RV water pump from back feeding into the city water system.
MrVan
Explorer
May 29, 2014
Do you have a manual valve at or near the city water connection where you can direct water to the fresh water tank? Maybe it isn't fully switch to the correct position. Or id there a check valve not working properly?
Old-Biscuit
Explorer III
May 29, 2014
Two ways water can get to fresh water tank while hooked up to city water
1) If you have valves/switches on a water panel the 'fill' valve could be leaking thru
2) Internal check valve of on-board pump is leaking back thru pump to tank

***If you have gravity fill forget #1. It's the pump check valve leaking.

You can disassemble pump and try to flush any debris, replace the internal check valve or install an in-line check valve in suction line to pump.
Sometimes just running pump will clear and debris holding check valve open.
Use it the rest of your trip and then test next trip/at home.

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