Extremely hot day finds recorder in church? On the contrary! (8)
I believe the answer is:
scorcher
'extremely hot day' is the definition.
'church? on the contrary' is the wordplay.
'church?' becomes 'ch' (common abbreviation).
'on' is an insertion indicator.
'the contrary' becomes 'scorer' (I can't explain this - if you can you should believe this answer much more).
'ch' going within 'scorer' is 'SCORCHER'.
'finds recorder in' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
(Other definitions for scorcher that I've seen before include "sweltering day" , "Informally, a really hot day - it burns!" , "burner" , "for example, really fine" , "Brand, perhaps" .)