As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
TEN MIN AFTER TAKEOFF THE RED LIGHT IN THE APU FIRE SHUTOFF HANDLE ILLUMINATED. THERE WAS NO RINGING OF THE FIRE BELL IN ACCORDANCE WITH QRH. THE APU FIRE HANDLE WAS PULLED AND APU BOTTLE DISCHARGE BUTTON PUSHED. THE RED LIGHT IN THE APU FIRE HANDLE REMAINED ILLUMINATED. EGT WAS 100C WHEN THE LIGHT CAME ON AND SLOWLY DECREASED DURING THE FLIGHT. *S/D* REPLACED APU FIRE & OVERHEAT DETECTION POWER UNIT MM.