Boiler going in benefits root crop (7)
I believe the answer is:
turnips
'root crop' is the definition.
'boiler going in benefits' is the wordplay.
'boiler' becomes 'urn'.
'going in' means one lot of letters goes inside another.
'benefits' becomes 'tips' (tip is a kind of benefit).
'urn' inserted within 'tips' is 'TURNIPS'.
(Other definitions for turnips that I've seen before include "Neeps" , "Root vegetables" .)