A320
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Flight Crew FLC complied w / Automation / Advisory; Flight Crew Returned To Gate; General Maintenance Action
Aircraft
During taxi out (APU was shut down after engine start) prior to takeoff; APU exhaust fire was reported by an aircraft behind us. We then found that APU fuel valve had failed to close after shutdown. We pressed APU Fire and pulled APU fuel circuit breaker per mx control to no avail. Thanks to good work by [the] fire department no evacuation was required as the fire was extinguished. We taxied safely back to gate followed by the fire trucks. We never received any ECAM or cockpit warning of the APU fuel valve disagreement. The only cockpit indication was found when we selected the fuel system page where we were able to see the APU fuel valve stuck in the open (or not closed) position with the APU shut down.I believe ECAM should have caught this; but am still researching. Should we check the fuel page before takeoff?
A320 Captain reported returning to the gate after shutting down the APU because of an APU exhaust fire.