Press the button, watch the LED be on for a time (heating) and then self turn off).
Here is an example of a latch circuit based on an NPN-PNP pair, which then powers an LED and 100Ohm Load simulation of the kettle heating element. A third NPN transistor has an RC filter on it's base. Once the C reached Vth(base) for the NPN then the NPN switches, discharges the base of the first NPN latching the circuit off. The RC time simulates the time it would take for water to boil (in practice you would have a thermostat which would operate the same way in terms of switching once the temperature reached a threshold).
