Is there anyway I can test the thermcouple to prove it's the fault?
We had a discussion about this 2 - 3 months ago. I measured 28 milli-volts when my thermocouple was hot and not connected. The resistance of my thermo couple was 0.2 ohms.
You will need the lowest voltage range on your digital test meter. Mine is 400 milli-volts.
Connect one probe to the outside of the thermocouple, the other to the inner connection.
Because the voltage generated by the thermocouple is very small, the centre contact and it's mating surface must be very clean & bright. The connection also has to be screwed up tightly, but not too tight to strip the thread
As previously mentioned, you do all this at your own risk. If you don't feel competent, you should call in your local friendly RGI.
HTH