As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING INITIAL CLIMBOUT, RECEIVED A FIRE WARNING FOR NR 3 ENGINE. EXECUTED EMERGENCY PROCEDURES, DISCHARGED FIRE BOTTLE AND RETURNED TO SFO. *S/D* FIRE WARNING PROBABLE CAUSE WAS DUE TO FAILURE OF MANIFOLD CLAMP BETWEEN THE PNEUMATIC MANIFOLD AND HIGH STAGE VALVE. CLOSE VISUAL INSPECTION INITIATED FOR I800 HOUR INTERVALS.