The stars were at the event Thursday to promote their new animated movie Trolls in front of thousands of fans.
Hollywood Life reported they pressed a large, novelty button, but it failed to illuminate the famed observation wheel after a countdown.
Timberlake and Kendrick laughed at the epic fail, trying several times to light up the tourist attraction. The pair looked relieved when it finally burst into rainbow colors.
The recording superstar posted photos and a video from the event on his Facebook page.
“Lighting up the London Eye for #DreamWorksTrolls!” he captioned the images, one of which showed him and Kendrick looking surprised when the button didn’t do what it was supposed to.