Current regulator right: East German in warm (8)
I believe the answer is:
rheostat
'current regulator' is the definition.
(I've seen this before)
'right east german in warm' is the wordplay.
'right' becomes 'r' (common abbreviation).
'east german' becomes 'ost' ('east' in German).
'in' is an insertion indicator.
'warm' becomes 'heat'.
'ost' going into 'heat' is 'heostat'.
'r'+'heostat'='RHEOSTAT'
(Other definitions for rheostat that I've seen before include "Electrical controller" , "The roast (anag.); electrical instrument" , "Variable resistance" , "Current controller" , "Variable resistor" .)