As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FDM 5964 BWI-IAD (1537 PHX LCL). LAVATORY FIRE WARNING IN-FLIGHT WITH THE WARNING EXTINGUISHING AFTER A PERIOD OF TIME. THE CREW REPORTED, INSPECTED THE LAVATORY AREA FOR SIGNS OF FIRE OR SMOKE WITH NONE NOTED. MX COULD NOT DUPLICATE, NO DEFECTS NOTED, OPS NORMAL.