Still the old-fashioned central heating (3)
I believe the answer is:
yet
'still' is the definition.
('yet' can be a synonym of 'still')
'the old-fashioned central heating' is the wordplay.
'the old fashioned' becomes 'ye' (I can't justify this - if you can you should believe this answer much more).
'central' indicates the central letters.
The centre of 'heating' is 't'.
'ye'+'t'='YET'
Can you help me to learn more?
(Other definitions for yet that I've seen before include "Still, even" , "Still, so far" , "Up to the present time" , "Up to this time and continuing" , "To this time, nevertheless" .)