As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CLIMBING THROUGH FL230 LT ENG FIRE WARNING ILLUMINATED. REDUCED POWER TO IDLE AND FIRE LIGHT EXTINGUISHED. IFE DECLARED. AIR RETURN TO DEPARTURE WITH UNEVENTFUL LANDING AND TAXI. SWAPPED LT & RT FIRE DETECT BOXES. INSTALLED A NEW LT ENGINE TAIL PIPE FIRE DETECT ELEMENT. NO DEFECTS NOTED ON GROUND ENGINE RUNS.