UA 3870 then TP 4392 at San Francisco
Xiamen → San Francisco → Boston
Timetable, San Francisco time
07:49UA 3870 from Xiamen at the gate
22:10TP 4392 to Boston leaves the gate
14 h 21 apart on the timetable
TP 4392 leaves 14 h 21 after UA 3870 arrives on the timetable: more than half a day, so not a connection we count.