Strike central heating snag (5)
I believe the answer is:
hitch
'snag' is the definition.
('hitch' can be a synonym of 'snag')
'strike central heating' is the wordplay.
'strike' becomes 'hit' ('hit' can be a synonym of 'strike'**).
'central heating' becomes 'ch'.
'hit'+'ch'='HITCH'
(Other definitions for hitch that I've seen before include "knot" , "Tether (rope); difficulty" , "Unexpected problem" , "Small problem" , "Pull up" .)