Welcome, my name is Rob and I will be helping you with your problem today. If anything isn't clear, please just ask me.
Different manufacturers use different terminology for different components.
This is then confused further, by them using abbreviations !!
FSD stands for Flame Safety Device, which is the same as a thermocouple.
It detects that the flame is lit and keepds the gas valve open.
If the flame goes out, it is detected by the FSD and cuts off the gas valve
If you need more help, please just ask
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