My face is diffusing warmth (7)
I believe the answer is:
cordial
'diffusing warmth' is the definition.
(cordial can mean warm or friendly)
'my face' is the wordplay.
'my' becomes 'cor' (both are expressions of surprise).
'face' becomes 'dial' (face of a clock).
'cor'+'dial'='CORDIAL'
'is' acts as a link.
(Other definitions for cordial that I've seen before include "drink with a fruity flavour" , "Warmly welcoming to the drink" , "Agreeable - drink" , "Friendly; fruit drink" , "Warm and friendly; drink" .)