United Flight 139 departed Denver at 1:19 p.m. MDT and landed at Seattle-Tacoma International Airport shortly after 4 p.m. PDT, The Denver Post reported.
"The aircraft landed normally and we are working to re-accommodate customers," United said in a statement.
The incident came one week into the debut of United's non-stop route from Denver to Tokyo. Boeing's Dreamliner, which went into service Oct. 26, 2011, was grounded by the Federal Aviation Administration from Jan. 16 to April 26 because of problems with the aircraft's lithium-ion battery system.
Passengers posted on social media websites the Flight 136 had just begun to cross the Pacific Ocean when it turned around and headed for Seattle.