Release pent-up feelings (3,3,5)
I believe the answer is:
let off steam
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">release pent-up feelings</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for let off steam that I've seen before include "Get rid of pent energy" , "Give vent to anger" , "Give vent to one's emotions" , "Vent one's anger" , "release pent-up energy" .)