Wednesday, November 29, 2023


Ask Dave: Water fills my fresh water tank when it’s hooked to city water

Dear Dave,
I have a 2018 Thor Chateau 24F hooked to campground water. Yesterday I noticed water coming from the fresh water tank overflow. I cut the shore water off and it stopped. I turned on the pump and the water is working OK. Is there a check valve or something that has gone bad? —Charles

Dear Charles,
From what I can see from brochures available on the Thor site, your rig does not have a city water diverter valve. This is a switch that will divert pressurized water from the outside campground source to either the interior plumbing, or it will switch over and fill your fresh water tank without the need to disconnect the hose and use a gravity fill. Rather, it has a city water connection on the side and a gravity feed similar to this, right?

With the diverter valve, the valve could go bad and not switch over completely. This would fill your tank and come out of the overflow. This would require a new valve.

Check water pressure coming into the rig

Evidently, you are getting water pressure coming back through the onboard water pump through the check valve. The first thing I would look at is the water pressure coming into the rig from your outside source. Most campgrounds will have higher pressure, especially the closer you are to the well pump. It might be higher than the pump can handle. I would check the pressure and install a pressure regulator that will reduce the pressure to 40-60 psi.

If you are already doing this, or the pressure is not too high, then I would look at the check valve of your water pump. It is located on the front of the pump. There will be a red wire coming off it, if it is a Shurflo pump such as the one in the photo below.

Sometimes you can fill the fresh water tank with hot/warm water and run the pump for a few minutes and “cycle” it several times. It is possible there is a buildup of calcium or lime and it is not closing properly, or the seal could be getting dry.

If that does not fix the problem, I would take the pump out and pull off the pressure switch and see if it can be cleaned out. There are three screws and it has a rubber bladder and spring that can be taken apart and cleaned. It, too, can have calcium, lime, and grit keeping it from sealing.

Otherwise you can purchase a new one on Amazon for about $30 and replace it. Here is the link.

Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club.

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Dave Solberg
Dave Solberg
Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. He has been in the RV Industry since 1983 and conducts over 15 seminars at RV shows throughout the country.



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Tommy Molnar (@guest_171781)
1 year ago

We had this happen a couple of years ago. After conferring with the ‘college of YouTube’, we cycled our water pump on and off a few times and that solved it. Whew!

Bob p (@guest_171753)
1 year ago

Had the same thing happen in our 18 year old Mountain Aire. Since his unit is not that old it’s probably an over pressure situation as you suggested. I carry a pressure gauge and check dead head water pressure before hooking up my hose. Since I bought a good pressure regulator I no longer have to use the kind that regulates pressure by cutting the flow. Those 7.98 regulators work but you suffer for it in the shower. Lol

Jesse Crouse (@guest_171761)
1 year ago
Reply to  Bob p

Good advice Bob. Always check all utilities in a campground before you hook-up to them.

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