Whirlpool touch control hob

Hi I will be going to above appliance on monday I dont have the model or service no. as the customer was not at home when she rang but will ring today with it.The prob is she turns on one of the elements and it just gets warm and it wont heat up anymore even when pressing the plus sign.Would I be right in thinking its the control and not the element.This is my first call to a touch control hob so any advice will be appreciated.How do I get to the control is it from underneath or top and is there a seperate control for each element.As I say ANY advice will be greatly appreciated.

Tom.