Assistance required to cover top of charcoal burner (4)
I believe the answer is:
acid
'burner' is the definition.
(an acid might burn things)
'assistance required to cover top of charcoal' is the wordplay.
'assistance required' becomes 'aid'.
'to cover' is an insertion indicator.
'top of' suggests taking the first letters.
The initial letter of 'charcoal' is 'c'.
'aid' enclosing 'c' is 'ACID'.
(Other definitions for acid that I've seen before include "It turns litmus paper red" , "Drug LSD (colloq.)" , "Corrosive substance" , "scathing" , "It is neutralised by alkali" .)