US TV
Heder dropped out of the Will Ferrell-produced sitcom in March only days before production was to begin.
He allegedly left over "creative differences with the character", Heder's rep told Entertainment Weekly.
Gethard will take on the lead role of a computer geek who chases his dreams and moves back in with his parents.
Chris Parnell and Horatio Sanz have signed to co-star in the project, further produced by Chris Henchy and Adam McKay.
Gethard will also appear in Ferrell's upcoming film The Other Guys.
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Tube Talk
'Bedlam': On set for the new seriesTube Talk takes a trip to the Bedlam set and speaks with star Lacey Turner.
US TV Interviews
'Mike and Molly' Reno Wilson Q&ADigital Spy chats to Reno Wilson about Mike and Molly's wedding and beyond.
US TV Ratings
'Duets' beats 'Touch' finale on ThursdayMeanwhile, CBS wins primetime with a lineup full of repeats.
2012-13 Season
'Sherlock's Lara Pulver joins new dramaLara Pulver will star in the new Starz series about Leonard Da Vinci.
