Turning a little heat up, nicking computer data (5)
I believe the answer is:
input
'computer data' is the definition.
(I've seen this in another clue)
'turning a little heat up nicking' is the wordplay.
'turning' says the letters should be written backwards.
'a little' says the answer is hidden in the clue (a little bit of the clue).
'tupni' can be found hidden inside 'heat up nicking'.
'tupni' backwards is 'INPUT'.
(Other definitions for input that I've seen before include "Signal fed to equipment" , "Provision of data" , "Contribution - data fed to computer" , "Signal feeding a circuit" , "Simple, without artifice" .)