Wow a good one. The tech was thinking you have the usual " Fresh water tank is overflowing."
The quick way to stop the pump is to pull the 12v fuse.
Now for trouble clearing.
1. Unplug from 110ac
2. Flip use/store to store
.....did the pump stop (you did put the 12v fuse back in, didn't you)
3. Turn the city water OFF
4. Check (operate 2 or 3 times) the fresh water pump switch, make sure it's off
5. Flip the use/store switch to ON
....did the pump start
6. If it did take the fresh water switch out of the panel (take a picture of the wires) and pull the wires off
....did the pump stop, if it did you have a bad switch maybe
More help is on the way, let us know.