Having no central heating is negative (3)
I believe the answer is:
not
'is negative' is the definition.
(thesaurus)
'having no central heating' is the wordplay.
'having no' becomes 'no' (I've seen this in other clues).
'central' says to take the centre.
The middle letter of 'heating' is 't'.
'no'+'t'='NOT'
(Other definitions for not that I've seen before include "In no way, never" , "It negates a word" , "Having close-cut hair" , "Negation of what follows" , "Negatory word" .)