Heard fireplace was wonderful (5)
I believe the answer is:
great
'wonderful' is the definition.
(I know that wonderful can be written as great)
'heard fireplace' is the wordplay.
'heard' shows a homophone (sound like).
'fireplace' becomes 'grate' (grate can mean a fireplace).
'grate' sounds like 'GREAT'.
'was' is the link.
(Other definitions for great that I've seen before include "Wonderful" , "Extensive; excellent" , "Marvellous; big" , "Brunel's third and last steamship" , "Large, fantastic" .)