On the subject of fuel, it's nothing new (6)
I believe the answer is:
repeat
'nothing new' is the definition.
(I've seen this in another clue)
'on the subject of fuel' is the wordplay.
'on the subject of' becomes 're' (re means regarding a certain topic).
'fuel' becomes 'peat' (peat is a kind of fuel).
're'+'peat'='REPEAT'
'it's' is the link.
(Other definitions for repeat that I've seen before include "Further airing" , "Quote from memory" , "Duplicate" , "Reiterate" , "Parrot" .)