Cooker installed in N America gets extended service period (6)
I believe the answer is:
novena
'extended service period' is the definition.
(nine-day period of prayer)
'cooker installed in n america' is the wordplay.
'cooker' becomes 'oven' (I've seen this before).
'installed in' is an insertion indicator.
'america' becomes 'a' (common abbreviation - e.g. in organisation names).
'n'+'a'='na'
'oven' put inside 'na' is 'NOVENA'.
'gets' acts as a link.
(Other definitions for novena that I've seen before include "Nine-day ritual" , "Roman Catholic devotion over nine days" , "RC prayers over 9 days" , "Services on nine successive days" , "Sequence of prayers" .)