⚠ Safety note: This guide involves working with electricity. If you're not completely sure about every step, stop and call a licensed professional. Before you start, always switch off the power at the breaker or close the main water/gas valve.
1 Prepare safe work
Unplug the appliance, shut off the water supply if there is one, and wait for the hot parts to cool. Prepare the manual for the exact model, a flashlight, and a dry work surface.

⚠ Warning: Do not open any part of the appliance that carries mains voltage, a capacitor, the heating element, or the refrigeration circuit. Leave that diagnosis to a qualified service technician.
2 Determine the exact symptom
Check whether the lid closes fully, because steam has to reach the thermostat. Clean any buildup around the lid and spout.

3 Check the most common cause
Descale it according to the manual and make sure the kettle sits level on a dry base. Do not immerse the base or the lower part of the kettle.
4 Remove the cause without improvising
Boil only the specified amount of water under supervision. If the switch does not turn the appliance off as soon as the water boils, stop using it.
? Tip: Take a photo of the starting condition and change only one thing at a time so you can tell what actually fixed the problem.
5 Reassemble and test safely
Reassemble all accessible parts and run a short supervised test. If you notice a leak, a burning smell, sparking, or a tripped protection device, switch the appliance off immediately and call service.

When to call a professional: If the job involves changes to the electrical panel, the main gas line, or load-bearing walls/beams — or if you're not sure how it will turn out — this is not a DIY task. Hire a licensed professional.