pyrostat

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An automatic sensing device that activates an alarm or extinguisher in case of fire.
• noun A high-temperature thermostat.

from The Century Dictionary.

• noun An apparatus for maintaining constancy of temperature; a thermostat; specifically, a thermostat for high temperatures.
• noun An automatic draft-regulator for chimneys, smoke-pipes, and smoke-stacks. See draft-regulator, under regulator.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun a thermostat designed to operate at high temperatures

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a thermostat that operates at very high temperatures