Gas Cooker hob Thermocouple keeps breaking down

[WSB]

Got a hotpoint gas cooker which is 9 months old.
Recently found that the main hob won't stay lit.
As under warranty got their engineer round who said it was the thermocouple and replaced it. Worked for a few days, then got the same problem.
Same engineer came a second time and replaced thermocouple again.
Worked fine for that day, then next morning got the same issues.
Have him booked for a third visit but am just interested to know what the reasons could be?
All is clean and we've been very careful when cleaning around that area.
It's really annoying but just wanted some info as to what could be the overall issue?
Thanks in advance.

 

[CBW]

I would say it’s either not producing the correct millivolts or the gas valve part is knackered.

 

[WSB]

I would say it’s either not producing the correct millivolts or the gas valve part is knackered.

Thanks.
Does each hob have its own valve, as the others are all fine?
It's strange that all was fine for 9 months.
Now this main hob (the biggest) works for a while with new thermocouple, then after a day or so, stops working again.
Wondering if something is going wrong whereby it damages the thermocouple.
Are these type of problems with gas cookers common?

 

[CBW]

Not something I’ve had heard about, but rarely deal with cookers, so could be a known fault on the Hotpoint. Each one has its own control, which when the voltage is applied keeps it open, not sure about individual gas valves tbh, likely misunderstanding from me.