By changing the fan heating element I caused a short circuit. Since then, the temperature light stays on for ever although all controls are at zero. I need to gain access to my NEFF (B1542N0GB/01) oven operation/temperature selectors to see whether there is a fault there but to do this I have to first remove the push-in/push-out knobs. How do I do this? I have taken the top of the oven off but it is not apparent how to remove the knobs and take out the selectors as there are no obvious screws to be removed. How do I proceed? I would be grateful for advice please