Crossword Genius

Released trapped air from (a radiator) (4)

Ross

I believe the answer is:

bled

(Other definitions for bled that I've seen before include "Seeped (into an adjoining colour)" , "Lost blood" , "Haemorrhaged" , "Showed effects of injury" , "Extracted blood as treatment" .)

I've seen this clue in The Times.
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