The Collaborative International Dictionary of English v.0.48:

Thermoregulator \Ther`mo*reg"u*la`tor\, n. (Physics)
   A device for the automatic regulation of temperature; a
   thermostat.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

thermoregulator
    n 1: a regulator for automatically regulating temperature by
         starting or stopping the supply of heat [syn: thermostat,
         thermoregulator]