Not working? That's bad (3)
I believe the answer is:
off
This clue is a double definition.
'not working?' is the first definition.
(switched off)
'bad' is the second definition.
(eg meat that's gone off is bad)
'that's' is the link.
(Other definitions for off that I've seen before include "Discontinued" , "Gone away or gone stale" , "Of food, begining to decay" , "Disappointing" , "Away, or beginning to decay" .)