Person fiddling with cold radiator (7)
I believe the answer is:
cheater
'person' is the definition.
(cheater is a kind of person)
'with cold radiator' is the wordplay.
'with' says to put letters next to each other.
'cold' becomes 'C' (eg on taps).
'radiator' becomes 'heater' (I've seen this before).
'c' next to 'heater' is 'CHEATER'.
'fiddling' is the link.
This may not be correct. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for cheater that I've seen before include "Person flouting rules" , "The race (anag)" , "Dishonest person" , "Rook" , "Person winning unfairly" .)