As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 1211 BOS-BUF, AIR RETURN TO BOS DUE TO A BLEED 1 OVERPRESSURE ON EICAS IMMEDIATELY AFTER TAKEOFF. CREW COMPLIED WITH QRH PROCEDURES AND ISOLATED THE BLEED. THE TECHNICIAN ON T/S FOUND NR 1 BLEED OVERPRESSURE SWITCH MUSCLE LINE DISCONNECTED. RE-INSTALLED MUSCLE LINE PER FIM 36-14-00-810-808-A00.