Help - Bad Check valve? City water filled fresh tank

[teejaywhy]

2019 Nash 23D Travel Trailer

We arrived at camp last night and hooked up to city water. This morning, I went outside and noticed water dripping from my fresh water fill port. Prior to arrival, I had perhaps 15 gallons in the fresh water tank for travel. Now it is full to overflowing!

So I assume, a check valve has failed - allowing water from the city water input to fill my tank?

I know the water pump typically has a check valve built-in (Shurflo 4008) (?). Is there a second one? Would seem strange that TWO check valves would fail, but maybe there is not a standalone check valve - Not seeing anything between the hose coming from the tank and the pump, nor from the pump to the T into the PEX water lines.

I shut off the city water and turned on the pump to pump out some water from the tank. The pump seems louder than normal and is making a loud vibration. Perhaps an indication of a stuck check valve that is only partially open?

PS: Assuming I may need to replace the pump, what's the recommended latest/greatest? Also, would it be a good idea to install a dedicated check valve? (my popup had one).

THANKS IN ADVANCE for any help. Will be out and about today, will check back in this evening.

[joelc]

I had the check valve leak in my pump and when I was connected to city water the tank filled up. My fix was simple. After the pump, I installed a shut off valve. When I am using the city water I have it off and when using the pump, I open it. Remember to put in in so it will be blocking the water from the RV to pump.

[teejaywhy]

THANKS EVERYONE FOR THE SUGGESTIONS!

Ok, so I disconnected the city water, opened some faucets to drain / relieve pressure. Cleaned out the pump filter screen (it wasn't dirty at all, just a few grains...) then turned on the pump and ran some water.

Side issue/ other issue: Don't know what causes the pump to make a loud clattering/hammering noise, but I remember this happened once before and if I remember correctly, I just opened the fill port cap and it went away (?) So this time I opened the water tank drain and let out about a gallon of water. Now the pump has returned to quiet operation. Perhaps when the tank is overfilled, some vaccum created? not enough air in the tank? I dunno...

Anyway... I have now turned off the pump and turned the city water back on and now I wait to see if the tank overflows again..

Thanks for your help everyone. I will reply back if this works or not.

Even if this works, I think I will add an outboard check valve because it sounds others have had this same problem.

[Boomerweps]

Had same problem.
Disconnect the city water.
Run the pump for a while and use the water in your FW tank.
The seals in the pump should reseat themselves and function as check valves.
It can be as simple as having the flow pressure clear any minor debris and reorient the seals as designed.
I previously almost never used the pump and had the overflowing FW tank problem three camps. Read here about running the pump could fix it and it did.

[12th_Man_Fan]

Sometimes just running the pump for a few seconds will remove the trash from the check valve. Give it a chance to see if it is fixed after running the pump before replacing.

[CA_Traveler]

You can add a better quality check valve to the tank line.

[dougrainer]

Travel Trailer the only check valve IS the Water Pump. NOT a replaceable part in pump. You have to buy new pump. Doug