Water-heater bloke heard (6)
I believe the answer is:
geyser
'water-heater' is the definition.
(hot spring that boils water)
'bloke heard' is the wordplay.
'bloke' becomes 'geezer' (synonyms).
'heard' shows a homophone (sound like).
'geezer' is a homophone of 'GEYSER'.
(Other definitions for geyser that I've seen before include "Spring spurting hot water upwards" , "Intermittent hot spring" , "A jet of hot water from natural spring" , "Gas-fired water heater" , "It gushes steam and hot water" .)