He makes things hot for his employer (6)
I believe the answer is:
stoker
'his employer' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he makes things hot for' is the wordplay.
I cannot quite understand how this works, but
'he' could be 'ker' and 'ker' is found in the answer.
'for' could be 'to' (eg both can mean 'in the opinion of') and 'to' is found in the answer.
A single letter 's' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for stoker that I've seen before include "Bram - - , Dracula author" , "Furnace filler" , "Boilerman" , "one adding fuel to the fire?" , "One tending furnace" .)