Neglect furnace temperature (6)
I believe the answer is:
forget
'neglect' is the definition.
(I've seen this before)
'furnace temperature' is the wordplay.
'furnace' becomes 'forge' (forge is a kind of furnace).
'temperature' becomes 't' (abbreviation).
'forge'+'t'='FORGET'
(Other definitions for forget that I've seen before include "Dismiss from the mind" , "Be unable to remember" , "Slip one's mind" , "Stop remembering" , "Stop thinking about" .)