As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT RETURNED TO BASE AFTER NO REAR BAY OVERHEAT LIGHT ILLUMINATED. UPON INVESTIGATION, FOUND THE MIXING VALVE HAD SEPARATED AT THE FLANGE POINTED OUT IN THE ENCLOSED ILLUSTRATION. THE VALVE SEPARATION ALLOWED HP AIR TO LEAK, ILLUMINATING THE OVERHEAT WARNING. REPLACEMENT OF THE VALVE SOLVED THE PROBLEM.