The stove has a thermostatic control designed to turn off gas when no flame present to heat the little thermostat - usually holding in knob for 10-15 seconds will actuate full gas flow. If this is not happening after 15 seconds the control isn't working as designed, usually this is because there is grease or grime causing the problem. The burners should only be cleaned/changed by licenced gas fitter (although I have done mine several times).
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