The fact that it started working when you added water, says you were low. Check your tank and find where the water line to the tank comes out. On my motorhome it is on the street side. My motorhome can look level, but if it is slightly off level, it will stop pumping with a quarter tank of water.
1998 Pace Arrow 35 ft. F53 Ford V10 2014 Honda CRV toad
32 years mechanic at Delta Air Lines 15 year motorhome service manager. 3 popups....2 travel trailers....5 motorhomes....loved them all.