As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
BOS - ON CLIMB-OUT, OVERHEAT LIGHT ON B-LOOP STAYS ON. SINGLE LOOP SELECTED. AREA OVERHEAT LIGHT OFF WHEN PACK FLOW CONTROL VALVE CLOSED. RETURN TO BOS. FOUND PLUG MISSING FROM DUCT FWD OF NR 2 PACK VALVE. RE-INSTALLED PLUG AND RAN NR 2 PACK. ALL CHECKS OK.