Bimetal tongue or diaphragm valve. Been around for at least 100 years and
there must be at least 50 versions of this doing things from setting
mixture in small engines (automatic choke) to syrup and liquid food mixing
(including water etc). Some come with a knob so you can preset the desired
temperature. I think that some high end bathroom fixtures have this built
in. An Italian manufacturer comes to my mind (but I forget the name).

Peter

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