Blackened and marked around the central heating (8)
I believe the answer is:
scorched
'blackened' is the definition.
('scorch' can be a synonym of 'blacken')
'marked around the central heating' is the wordplay.
'marked' becomes 'scored' ('score' can be a synonym of 'mark').
'around' indicates putting letters inside.
'the central heating' becomes 'ch'.
'scored' placed around 'ch' is 'SCORCHED'.
'and' acts as a link.
(Other definitions for scorched that I've seen before include "Seared" , "Fruit-growing area" , "Charred, blackened" , "Slightly burned" , "got very heated" .)