Yes. The thermocouple for the flame failure device has failed. Based on your diagnosis "it is because the knob controlling it will not stay down," may one suggest you get a competent person to change it out.
If you are going to do it yourself, you will need the make and model of hob to order spares
ewerwq
April 2018
Automatic Answer
We may have found other answers which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix gas cookers.