Back a favourite I'd found not so hot (5)
I believe the answer is:
tepid
'not so hot' is the definition.
(I've seen this in another clue)
'back a favourite i'd' is the wordplay.
'back' says the letters should be written in reverse.
'a favourite' becomes 'pet' (synonyms).
'pet' backwards is 'tep'.
'tep'+'id'='TEPID'
'found' is the link.
(Other definitions for tepid that I've seen before include "Luke warm" , "without passion" , "Showing little interest or enthusiasm" , "Not very enthusiastic" , "lacking enthusiasm" .)