B737 Next Generation Undifferentiated
Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Flight Crew Type 704
Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Fuel Issue
Flight Crew Diverted; Flight Crew Landed As Precaution; General Maintenance Action
Aircraft
We had the same aircraft for three legs on the same day. On the first leg we experienced problems with the center tank fuel pumps not functioning properly and then fuel transferring into the center tank once they were turned off. We notified Maintenance of this and they said to check it again on the way to ZZZ. We experienced the same thing on that leg and wrote it up again. In ZZZ Maintenance said to check it again on the way to ZZZ1. On the way to ZZZ1 it occurred again but this time so seriously that we were unable to control where the fuel was going. It was quickly getting out of balance and we were not able to control that so we diverted into ZZZ2.
This was the 3rd leg of the day on this aircraft. We had written up the left center fuel pump light on the first leg because it was on. When in ZZZ1 we added more fuel to the center tank and was told to monitor. On the way to ZZZ the fuel pump light did not come on; however some of the fuel from the wing tanks entered the center tank. At ZZZ we filled up the center tank and was told to monitor it again. We had about 2;000 lbs in the center; 19.0 planned gate. Took off with 6 pumps on. On the climb out; the left center fuel pump light came on when there was still around .28 left in center tank. We turned the left pump off and kept the right center on. At that time no fuel was being used out of the center even with the pump on and was creating an imbalance so we turned the right center pump off. As we did that; the left wing tank quantity rapidly decreased and the center tank quantity started increasing. At one point the center tank had accumulated around .95 (where it had previously been around .25 when we turned the right center pump off). Because the fuel was rapidly moving out of the left and into the center we decided to divert to ZZZ2 as we were abeam and make a safe landing.
B737NG flight crew reported diverting to an alternate airport when they were unable to control fuel transfer from a wing tank into the center tank.