Fuel cut — not keeping hot (3)
I believe the answer is:
gas
'fuel' is the definition.
(gas is a fuel)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for gas that I've seen before include "16 (US)" , "Hydrogen or methane, say" , "Empty talk (colloq.)" , "natural resource" , "Wind" .)