Fresh water tank overflowing

Just keep using your pump.........

GO thru a whole fresh water tank and allow it to flush pump internals

Sanitizing gets rid of bacteria.

Hard water causes scaling.......flushing/using helps keep the scaling to a minimum.

Shurflow has an in-line check valve. Barbed so you just cut SUCTION line into, slip it in place and secure it with hose clamps
Suction line is used so that pressure inside pump doesn't bleed off pressure switch (discharge side pressure would and pump would still continue to cycle)

allenm wrote: "I do have a high-flow pressure regulator installed at the campground spigot. Maybe there is just too much pressure in the lines?"

What is the water line pressure going into your RV? (if you know) Any water pump cycling without water use indicates a leak somewhere. As previously suggested, I'd start by removing the pump and/or the pump check valve and check for debris. In a 10 month old vehicle, there's a good chance that construction/assembly debris got in the tank/lines somewhere.


Chum lee

One pump cycle every 20 minutes is not what I would call excessive.

Ok - here's what I've done so far. Shutoff campground water and relieved pressure. Cycled pump a dozen times to lower water in tank until it quit overflowing. Then I left the pump switch on, and I didn't use any water. It comes on about every 20 minutes, so it's leaking internally.

It's a Shurflo 4008. Here's what the manual says "Lack of sanitizing is the number one reason for premature pump failure and poor performance over time. Lack of sanitizing will cause scale build-up on the diaphragm and valves, causing low flow and leak back occasional pump cycling with no faucets open or tank filling up when hooked up to city water".

Guilty as charged, but in my defense it's only 10 months old and it's been used regularly. When I get back home, I'll have to see if the dealer will take care of it under warranty, or I'll have to take it apart myself.

For now I guess it's not really hurting anything.

To test the water pump for leaks, shut down the city water supply and turn on the water pump. If the pump cycles on and off when all water taps are closed then in all likelihood the pump is at fault.

If it is the pump a fault it may be some grit in the internal check valve(s) in the pump which may only require some disassembly and cleaning.

Yes, either the check valve in the pump is bad OR the fill valve is not fully closing.

If you have a hand valve to switch from city to fill fresh tank.
It may be leaking past it. Open close that valve a number of times that may break a small piece causing a leak at that valve.

Or that valve may be needed to be replace.

Your 12v water pump is malfunctioning and allowing water to backflow into your fresh tank. The quick fix is to install a check valve in the output line of the water pump. If it's the pex line you can buy a sharkbite check valve and not require any clamps.