I am troubleshooting a gas hob where one burner is reluctant to light. When it is lit and I blow the flame out the FSD on that burner cuts off immediately, whereas the others take 5-10 seconds as normal. I have tested the thermoucouple for continuity and also some sort of mV output (when held over a candle!). Do you think this is an FSD problem or a thermocouple change?