Bimetallic Thermostat
I've managed to reset the device. 

There is an oblong piece of mettle set in a round space. This allows one to get a small piece of wire (none flexible, i.e. a pin) under the metallic strip and snap it up; it then becomes loose ish.

Ive tested it with a lighter and it clicks then becomes open circuit. 

I guess it's a one shot in reality, because it's not designed to be reset.

This quick fix will get you going until you can get a replacement part.