On 17/09/2016 09:01, Brian Gaff wrote:
I've often wondered how such things work. The ones with a coiled tube and a
thicker end with a knob on one end and thethicker end in the oven always
seem to be crude to me. I wonder why even modern ovens use this over the
electronic alternative?

The sensing end could easily be a thermistor but the electronic side
would have to endure a high temperature and you would need to drive a
gas valve as well as needing power.

A simple bulb of liquid which when expands has sufficient force to hold
off a valve seems incredibly simple and reliable to me.

Perhaps a thermopile? I have seen a gas fire use one in conjunction with
a conventional thermostat to turn the gas valve on and off.