Fuel putting out no heat and just the first hint of light (7)
I believe the answer is:
ethanol
'fuel' is the definition.
'out no heat and just the first hint of light' is the wordplay.
'out' is an anagram indicator.
'and' says to put letters next to each other.
'just the first hint of' suggests taking the first letters.
The first letter of 'light' is 'l'.
'no'+'heat'='noheat'
'noheat' anagrammed gives 'ethano'.
'ethano'+'l'='ETHANOL'
'putting' acts as a link.
(Other definitions for ethanol that I've seen before include "Kind of alcohol found in Athlone" , "Intoxicant in wine, spirits, etc" , "spirit" , "Ethyl alcohol" , "intoxicating stuff" .)