B777 Captain reported a gate return for load issues. Maintenance met the aircraft and informed the Captain that a tail pipe fire was reported. After engine runs; a faulty fuel valve was diagnosed and the aircraft was removed from service for repair.

Narrative

Initially dispatched with Aircraft X. Flight returned to gate to address loading issue. Upon gate arrival; Maintenance met aircraft. We were told that ramp service had reported noticing flames from the right engine as we parked. All cockpit indications were normal during gate arrival and engine shutdown. Nothing abnormal observed or reported from flight deck. Maintenance came on aircraft and advised that an engine run was necessary. Engine run was performed and the engine started and operated normally. Upon shutdown; it was noticed that the fuel flow did not initially go to zero. After approximately 1 minute; the fuel flow went to zero and the engine shut down as commanded. There were no irregular procedures required in the cockpit. During the period of time awaiting the engine to shut down; maintenance observing the engine run also commented about flames from the rear of the right engine. No cockpit indications of abnormality beyond the fuel flow issue. After observing the engine run; maintenance determined that the engine had a faulty fuel control valve on the right engine and that the fix would be lengthy. Therefore; the flight was delayed to the next day and operated with a different aircraft. No specific safety issues noted on this flight. However; report filed to factually account for the situation.