If the temperature on your EKG is fluctuating, this is usually caused by limescale build-up around the temperature sensor. We would recommend descaling your kettle to resolve the issue.
To get rid of limescale, mix a 1-to-1 solution of water and white vinegar (250 mL of each) and pour it into your kettle. Let it sit overnight and in the morning, heat your kettle to a boil for 5 minutes (turn the hold switch off if it's on) and let sit for at least another half-hour. Afterwards, rinse out the kettle with fresh water to get rid of residual vinegar. If you notice lingering traces of vinegar, fill your kettle and add a tablespoon of baking soda before heating again. Baking soda does a good job of neutralizing the scent of vinegar and will also help remove stubborn limescale stains.
If limescale stains remain after this process, citric acid is a more powerful, and safe, alternative to vinegar and should remove any residual limescale.