E5 indicates a power problem to the hob.
If the supply to the hob is ok it would suggest a fault with the power board inside the appliance.
The power board will be an expensive part and the part required will depend on the product number of your appliance.
Click here for an example of an AEG hob power board
This isn't the board for your appliance, as far as I know, it's an example of the likely price.
Given the cost of parts, I'd suggest checking www.repaircare.co.uk for a fixed price parts and labour quote.
Check the supply and the connections to the hob, ensure none of the connections are broken.
If they are all ok, then the fault is within the appliance and the most likely part is the power board.
Hope this helps
Let me know how it goes or if you need more help