Over filling

you overfilled the tank and it spilled out. seems routine to me. did it somehow get switched to tank fill by mistake?
bumpy

The tank has a vent in the top to let air in/out. When filling air and then water comes out the vent.

I have a coachman a couple years newer than you and I have done this twice. One was while filling and not paying attention when it filled up. The other was when I thought I had my water switch on city but it was on tank fill while we took a walk around the CG. The water overflowed for at least 15 minutes. No problems except for a lot of water wasted and a muddy mess around the motorhome. The water just goes out the top vent or overflow and onto the ground.

Danford50 wrote:
I connected my water hose to city fill

This is ambiguous. There is a city water inlet and a tank fill inlet. (Not all rigs have a separate tank fill inlet.) If you connected to the city water inlet, then you do, indeed, have a backflow preventer in the water pump that has failed. If you connected it to the tank fill inlet, you need to stand there while it fills till water comes out the inlet and vent, then turn the water off.

The units without a separate tank fill inlet have a valve that you turn to switch between city water and tank fill. If that valve is turned wrong, that will happen.

Just reread your post-I answered a question you didn't ask. On mine, if yours is similar-has a switch or lever where the water fill is. this must be turned to what you want-whether city or tank fill. Mine is blue and about 2" long.

Where was the water coming out ? I have never heard of " city fill " , are you sure that is what it sez ?

Sounds to me like there is a check valve issue with your water pump. This happened to me once and I had to replace the pump.

This is a common question asked on a Jayco Facebook group. Many times it is the pressure check valve on the pump especially if the pump hasn't been used for some time. The check valve gets dry and sticks. Pumping some water from the freshwater tank can help to prevent that. That check valve is located on the power input end of the pump.

rrupert wrote:
This is a common question asked on a Jayco Facebook group. Many times it is the pressure check valve on the pump especially if the pump hasn't been used for some time. The check valve gets dry and sticks. Pumping some water from the freshwater tank can help to prevent that. That check valve is located on the power input end of the pump.

^this

1. Run some water through the faucets using only the pump.
2. If that doesn’t fix it you may have to take the pump apart to clean a piece of debris out.
3. Failing that, you can usually buy a rebuild kit (new diaphragm) or new pump.

OP can come back and explain. Then it would be clear….er, maybe?