Martin gas stove, sensor fell off?

[Jotel me this]

Hello. I was looking at my gas fireplace and noticed in the top grate there are two white wires. I didnt think too much of it until I looked into the grate and saw the flue. I also noticed a spot where it appears something circular came off of the flue. Putting two and two together, I believe a sensor fell off/broke off of the flue.

What does this sensor do? The fan control is behind the bottom grate. Does it turn on the fan if things get too hot, or an emergency gas shut off of sorts? Any idea what the sensor is and where to buy a replacement? Thank you!
Model: 300 DVBNV




Looking into top grate, I see two wires:


Looking closer, it looks like there's a sensor at the end of the wires. I exploded the view to make it easier to see as well:


And on the flue, it looks like this is where the sensor attached:


I found this kit on Amazon, and it looks like it comes with the sensor, but I dont know what the sensor even does.


Update..
I found this Youtube video:


And the guys shows the sensor is supposed to go on the side of the firebox. More pics of my fireplace:

I took off the top grate and found the sensor:


Problem is, the side of the firebox also has a spot where a sensor should go... and a spot on the flue? Were there two??


It looks like the sensor is broken somehow. How could this happen? Maybe the previous owners damaged it somehow?



So I guess the question is, does this sensor go on the flue, or on the side of the firebox?

 

[Lennox65]

Can you provide a picture of the rating plate? The exact model number and year of manufacture would help in finding the correct manuals.