City water leaking into fresh water tank?

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roaminrebelles

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Joined
Jul 12, 2020
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18
Im positive that that?s what?s happening, how is this possible??? I had to take the cap
Off the fresh water outlet to let the overflowing water come out, obviously also worried about water damage to the rig but no visible signs as of yet. I?m thinking it?s a slow leak, my sensor on the freshwater tank has been saying it was getting full but I couldn?t understand how, where could this leak be coming from? It?s not the city water intake that is leaking, I already pulled that out and checked
 
A couple of things that might help people help you: What kind of rig is it (brand, model, type??)?  Is this happening when you are not hooked to a shore water supply, or only when you have shore water hooked up
 
Sorry, I?m in a 1996 Thor hurricane. And it is happening while hooked up to shore power, so you said the water pump? I haven?t had this rig very long, was messing around with the water pump the other day when I noticed the freshwater sensor said full. Unplugged from city water, turned faucets in and pushed the water pump switch, and nothing came out, assuming it?s broken.
 
And I believe it is only happening when hooked up to city water, it was empty when I bought it two months ago, have been hooked up to city water and shore power since then.
 
Ok I saw your comment on my related post about it possibly being a water diaphragm, thank you, I will look into that
 
That has happened to me twice and both times I needed a new water pump. 

Even if you are not using the water pump, water from the city water inlet can get through a defective diaphragm in the pump and fill the fresh water tank.  Then it will overflow and you will have a flood on the ground.
 
Thanks!!! ANOTHER thing to fix on this old rv hahaha ??? my poor wife, if she had a choice she would have set this thing on fire by now lol
 
If you can somehow get the old pump running and pumping water, try cycling it on and and off a few times, that may dislodge debris and cause it to seal.  First thing to check is that there is voltage supplied to the pump.
 
There are two possible paths for water to get into the tank from the city water inlet, depending on how the RV is plumbed.  Just about all RVs are vulnerable to a failed water pump diaphragm, where water pushes backwards through the pump and into the tank.  The second one is only in RVs that have a city fill valve, which enables water from the city inlet to flow into the tank to fill it.  A defective valve will let water flow. The defect can be either an internal leak or simply that the valve doesn't fully close.

If your RV has the city fill option, then it is the #1 suspect as it is a fairly common defect as the RV ages.  If not, I'd suspect the pump.  You can insert a check valve on the intake side of the pump to permanently eliminate that possibility. You can also make a temporary test by disconnecting or closing off the pump intake hose or tube in some fashion.  If that stops the tank-filling, you know you found the problem.  If you have the fill valve, replacing it usually is easy enough if you can get at it. That accessibility varies by RV, though.  The valve may be a simple on/off or a "3-way" diverter valve. It's not a unique RV part - just a standard plumbing fixture.
 
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