Stick nothing cold up on top of grill (5)
I believe the answer is:
cling
'stick' is the definition.
(I know that stick can be written as cling)
'nothing cold up on top of grill' is the wordplay.
'nothing' becomes 'nil' (eg nil is zero in football).
'cold' becomes 'c' (eg on taps).
'up' is a reversal indicator (in down clue: letters go upwards).
'on top of' says to take the initial letters.
The first letter of 'grill' is 'g'.
'nil'+'c'='nilc'
'nilc' in reverse letter order is 'clin'.
'clin'+'g'='CLING'
(Other definitions for cling that I've seen before include "act like limpets" , "Hold tightly, become attached" , "Be emotionally over-dependent" , "have emotional attachment?" , "Keep hold" .)