My partner has a heater for heating wax that is used for waxing legs and other body parts. She told me it stopped working; it does not heat up anymore.
When I opened the device and looked at it I found that the temperature is controlled by an NTC. When I measured its value, my meter said that it is open-circuit.
However, when I heat the NTC with a hot air gun, its resistance drops to a few kOhm.
When I let it cool down, its resistance increases and when it reaches 32 kOhm, it suddenly goes open-circuit.
I've repeated the heating and cooling cycle a few times to make sure that it isn't a fluke (although I am using a Fluke multimeter).
I've never seen an NTC behave like this; the resistance normally increases until it reaches its nominal value at room temperature.
Is this a special NTC or is it just broken?
I haven't been able to look at the NTC itself, because it is built into the device and I don't want to take it further apart unless I am pretty confident that the NTC is broken and needs replacing.
The NTC is soldered to two leads and is inside heat-shrink. The assembly is wrapped in transparent light-brown-yellowish adhesive tape. I assume that this is heat-resistant adhesive tape.