What is this weird component in my new hot air handle?

[Joebeazelman]

While probing the wires on a new handle for my Quick 856D hot air station, I got confused wondering why the reed switch is in series with the heater instead of the thermocouple like my original handle did. When I pulled back the terminal tabs for further inspection, it turns out the reed switch was indeed wired in series with the thermocouple but hidden inside a thermal sleeve.

Now I am left wondering what is the weird component I mistook for a reed switch. It's hard to read the inscription, but it says YCW on one side and 250V on the other. Any clues?

[nigelwright7557]

Probably a temperature sensor, maybe a thermistor.

[themadhippy]

what is this looks suspiciously like a thermal fuse

[Joebeazelman]

Bingo! Thanks. Just did a search for "metal thermal fuse" and found several that looked like it. This is the first time I've seen one inside a hot air wand. I wonder if it has any advantages.

[helius]

The main advantage is preventing fires. If through some fault, the heater is energized without airflow, the temperature of the handpiece will rise until the plastic melts and ignites. There are videos of this happening to (badly designed) hot air stations that are switched off; but it is a potential fault with any unit left switched on. The temperature control loop with the thermocouple does not provide fire safety: something more reliable is required.

These thermal fuses also find application in plug-in power meters such as the Kil-A-Watt where they are used for similar reasons.