As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
RETURNED TO GATE DUE TO A SMOKE AND BURNING SMELL AT AFT CABIN AREA. INSPECTED AND FOUND SMELL COMING FROM RECIRCULATING FAN. REMOVED AND REPLACED RECIRCULATING FAN PER BOEING M/M. RETURNED TO GATE A SECOND TIME DUE TO A BURNING SMELL. REMOVED AND REPLACED WATER SEPARATOR BAGS, AND LT AND RT HEPA FILTERS. RAN BOTH PACKS AND NR 2 ENGINE, NO DEFECTS NOTED.