The glass section of the washing machine becomes at least warm if not hot during a hot water wash. You can feel the glass area with your hand when the procedure is going on to see if it is warm. If the glass section remains cold to your touch it definitely indicates a faulty heating element. Another sign of a faulty heating element is the non stopping wash process. Some times the washer refuses to go to the next cycle and continues the wash cycle till you stop it. This happens when the water does not acquire the pre set temperature.
The only sure way to tell if a element is faulty, even if all the above faults are present, is to use whats called a ohmmeter, a ohmmeter is a device used for testing all types of electrical values, including resistance between 2 conductive device. To test if a element is working or not a engineer would connect a ohmmeters live and neutral wires to the corresponding connectors on the element and check for a positive reading, no reading would mean a faulty element, the engineer would also use the ohmmeter to read across both terminals again and the earth terminal on the element but in this case a positive reading would mean a faulty element and a negative reading would mean no fault on the earth to live and earth to neutral connectors