the firebox in a complete overhaul that lasted from September 2001 to 2004. On September 9, 2004, the UP steam crew successfully test-fired the 4-8-4. It returned to operating service on November 10, 2004. On May 18–19, 2007, No. 844 teamed with Southern Pacific 4449 to pull the "Puget Sound Excursion", a round trip from Tacoma to Everett on BNSF Railway tracks. On June 25 and 26, 2010, it made an excursion trip to Milliken, Colorado's centennial celebration. In September 2012, the No. 844 locomotive was used in "UP 150", a celebration of Union Pacific's 150th anniversary celebration, hosted by the California State Railroad Museum (CSRM). During that time, No. 844's tender derailed on a tightly-curved track from the Union Pacific's Martinez Subdivision to the CSRM. The tender was rerailed at 7:30 p.m. In June 2013, the locomotive's gyrating Mars Light, installed in 1946, was removed because its mounting bolts had deteriorated. It was also announced that year that the 844 and 3985 would eventually be joined by a third steam locomotive: Big Boy No. 4014. After the 2013 season, the locomotive was taken out of service for boiler work required by a change in the water treatment. It spent 2014 in Cheyenne, then received an early 15-year inspection the following year. On June 16 and 17, 2016, the 844 was test-fired. On July 12, 2016, the Union Pacific Steam Team took the locomotive on a "break-in run" as a sort of all-systems check and dress rehearsal for its return to service. The run was described as a complete success. On July 23, 2016, it pulled the annual Cheyenne Frontiers Day excursion. On October 13, 2016, the Union Pacific Steam Team started its 18-day "Trek To Tennessee" journey: the restored 844's first major trip. In April 2017, No. 844 made its first run on the Oregon Short Line Railroad to celebrate the 92nd anniversary of the Boise Union Pacific Depot. Because of heavy snows and a wet spring, the trip was cut short and the engine had to run light across the Malad River because of a washed-out bridge. In December 2018, Union Pacific requested Federal Railroad Administration (FRA) waivers to exempt UP Nos. 844, 3985 and 4014 from federal Positive Train Control (PTC) requirements; in February 2019, the FRA officials responded that such waivers were not needed. On May 4, 2019, No. 844 participated in the inaugural run of