As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT DIVERTED TO KCMH DUE TO AN OPEN ILS MEL AND THE WEATHER CONDITIONS IN KDCA THAT REQUIRED AND ILS APPROACH. MAINTENANCE TROUBLESHOT THE FAULT AND FOUND THE MARKER BEACON AND GLIDE SLOPE SYSTEMS TO BE OPERATING NORMALLY AND ONLY THE LOCALIZER TO BE MALFUNCTIONING. MAINTENANCE FOUND THE VOR/LOC ANTENNA DIPLEXER-COUPLER TO BE AT FAULT IN THE VERTICAL STABILIZER AND REPLACED IT WITH NO FURTHER DEFECTS NOTED.