Warm up again (6)
I believe the answer is:
reheat
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">warm up again</span>' is the definition.<br/ ><span class="explanation-format__explanation">(to heat or warm up again)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for reheat that I've seen before include "Cook again" , "Of cooked food, give another go in the microwave" , "Jet engine afterburner" , "Process increasing jet engine thrust" , "Method of getting extra power from jet engine" .)