On a British water urn, how does the thermostat work?

How does a thermostat on a British hot water urn work?
Are they different from smaller American coffee makers? (They have big coffee percolators in the US too, for public meetings and large parties, but I've never taken one apart, and I don't know if they are the same as in England anyhow.)
Someone from England writes:

Does this sound accurate?
This strikes me as using a bimetal strip just to make a timer. Am I right and have you ever heard of such a thing? If one is not using electronics, how is an interval timer for a high current device like a water urn made?
Would it be done by running current *through* the strip, as it says above?
These urns, and coffee pots in the US do have a method for keeping the water at the same temperature, when the red light is on, hot but not boiling, and the particular urn being described has iiuc two modes, one that uses an interval timer, and one that does measure the temperature.
Does anyone know about this from a British pov?
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