Hello, my name is ***** ***** I will assist you with answers to your problem.
The problem you have is with a thermocouple... You will need to purchase the correct one for your system
They are relatively easy to change if you are technically minded; alternatively you should get an engineer or a Gas-Safe engineer to replace it
Thanks George, do you have diagram of how to replace this on an AGA S-Series Six-Four Gas Hob?
Sorry I don't, but it involves the removal of the cooker hob-top.. You could ask for a diagram/instructions at you local Aga supplier who should have access to all the models
Servicing, Installation & Users Instructions
I had this link to the document you require
Thanks George, that great.