Hey Spud,
We have the same year and model unit you do.
I’m thinking if you had the city water connected and you’re noticing the fresh water tank filling up and overflowing it could be due to a bad check valve on the water pump which is allowing the water past and into the fresh tank. The water manifold that directs the water flow in the wet bay could also be a source for the problem. If those Anderson valves aren’t lined up they might be allowing the city water to flow into the tank.
You could easily just switch the water source on the manifold between, City, Pump and Tank Fill and back to City and monitor if the fresh tank is still being filled. If it still is getting filled, you might need to check the water pump back fill valve. You can disassemble and clean the pump components out as that can sometimes help. If that doesn’t solve the problem the water pump might need to be replaced. You probably have the same water pump I have (ShurFlo 4008) and you can purchase those for under $100 on Amazon. Not a bad idea to keep a spare either.
As for the Anderson water manifold, those can be replaced and are bit more expensive than the water pump and a bit more complicated in the hookups. I just replaced my manifold due to a broken valve knob. I posted the information in this thread.
Busted water heater bypass valve
If you do opt to replace the Anderson manifold, you’d need to call Anderson to order the replacement as they don’t list the Vanleigh version on their website. They also won’t warranty the manifold even though it says a 5 year warranty. That warranty starts the day they made it not when you purchased the finished product. At least that what the Online Sales & Marketing manager told me last fall.
Good luck in the troubleshooting.
Stuart