As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SHORTLY AFTER TAKEOFF, IN-FLIGHT REPORTED A BRIEF ACRID ODOR IN THE FWD CABIN. DUE TO THE INABILITY TO IDENTIFY THE SOURCE OF THE ODOR, THE RAM TEAM ELECTED TO BRING THE FLIGHT BACK TO DEPARTURE FOR MX EVALUATION. MX FOUND THE L1 DOOR HEATER DEFECTIVE AND REPLACED IT. ETOPS CATEGORY 'B': DIVERSION OR TURNBACK.