Current heating unit with leads in assembly line (7)
I believe the answer is:
thermal
'current' is the definition.
(I've seen this before)
'heating unit with leads in assembly line' is the wordplay.
'heating unit' becomes 'therm' (I've seen this in another clue).
'with' says to put letters next to each other.
'leads in' says to take the initial letters (I've seen 'lead in' mean this).
The first letters of 'assembly line' is 'al'.
'therm'+'al'='THERMAL'
(Other definitions for thermal that I've seen before include "Warming" , "Related to heat" , "Concerned with high temperature" , "type of baths" , "Warm or hot - underwear?" .)