Q: I am on city water and my freshwater tank is filling up, what could it be?
A: Check valve for the water pump is failing. Since you have water in tank already:
1. Turn off city water and disconnect hose.
2. Relieve water pressure, open a faucet
3. Turn on water pump, when it stops, turn on a faucet.
4. Turn off pump, open a faucet.
5. Attempt steps 3 & 4, two or three times.
6. If you things go right, the check valve will reset itself, turn off pump (if not already done so), hookup city water, see what level is of freshwater tank (or empty it) and then check it in a few hours and see if it filling up again.
7. If it does not begin filling up again, it worked.
8. If it does begin filling up again, you will need to replace the check valve.