Date: 201604
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Regional Jet 900 (CRJ900)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class C ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Fuel Crossfeed
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Troubleshooting
Second reporter function: Pilot Not Flying; Captain
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Fuel Issue
Detector: Person Flight Crew
When detected: In-flight; Taxi
Result: Flight Crew Diverted; Flight Crew Overcame Equipment Problem
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: It was a normal taxi out and we were cleared for takeoff. As we were taking the runway we got a X FLOW PUMP caution message on the EICAS. We pulled off the runway and performed the reset procedure which did not fix the problem. After calling Dispatch and Maintenance we were told that we could defer this item. Under the direction of Maintenance Control we deferred this item. After it was deferred we re-ran the before takeoff check and then noticed that we had a fuel imbalance which we fixed by taxiing. The takeoff was normal and at 5;000 feet the fuel was balanced and things were normal. At about 10;000 feet we noticed that the right tank was getting lower on fuel faster than the left tank. We tried to balance it out by raising the heavy wing which did not work. The imbalance got to 2;100 lbs and we decided (along with Dispatch's approval) to divert for a precautionary landing. The turning and descending for our landing helped the situation. The descent and landing was normal and we landed with a fuel imbalance of about 500 lbs. Once at the gate we completed the shutdown check. We then wrote up the aircraft and talked with the mechanic and told him everything we did and turned the aircraft over to them.After this event; Captain got a call from the 900 fleet manager to check that the gravity X-flow valve worked and not to leave it on. By doing this he said that the tanks would eventually be in an imbalanced condition because the aircraft does not fly perfectly balanced. Then we re-read the MEL about 10 times and we realized that we had misinterpreted the instructions for the gravity X-flow valve. After reading line 3 in the MEL which states; gravity X flow valve must be OPEN; otherwise dispatch is not permitted. This sentence made both of us believe that the gravity X-flow was to remain open during all phase of flight which was wrong.When we realized that we had imbalance fuel issue; we went through Fuel Imbalance QRH. However; it did not direct us to review gravity cross flow procedure. After we read the procedure we realized that on the 900 you can only correct a fuel imbalance by applying rudder to the low fuel side and to shut the gravity X-flow off once the condition is fixed. We did not go through X FLOW PUMP QRH during flight; which would have directed us to go to gravity cross flow procedure. It was deferred on ground and the caution message was associated with the deferred item.  This misunderstanding of the MEL instructions ultimately caused us to divert. Along with Captain; I take flying this aircraft and the safety of my passengers very seriously. I regret that we had this misunderstanding during our operation. However; the situation was becoming worse in any second and thankfully we decided to divert before this problem became any worse. Along with Captain; I take full responsibility for what happened and out actions. We landed safely and hopefully this situation can be shared with other pilots to prevent it from happening in the future.


Second narrative: [Report narrative contained no additional information.]


Synopsis: CRJ-900 flight crew reported a diversion due to a fuel balance problem associated with misinterpretation of an MEL.