Demo mode has been activated. You can see de on the display or the hob does not get hot, even though it can otherwise be operated normally.
Please deactivate demo mode as described in the operating instructions.
If the problem cannot be resolved, disconnect the appliance from the mains power supply for approx. 1 minute.
To disconnect the appliance from the mains power supply, turn off the relevant circuit breaker or remove the fine-wire fuse completely. Or switch off the residual current device.