smeg dual fuel element replacement?

h,i i want to replace heating element in my smeg cooker (ref suk91mfa) but can some tell me as there is 2 elements in the cooker, should one of them still be working (no heat comes fom either of them) ie do i replace both of them? i can see one of them has brocken so obvious replacment required to one of them,but do i need to replace both? ie when ones not work, do they both not work? - thanks