Diagnosis
It's overheating and the thermal cut-out is doing its job. This is 99% a airflow problem caused by a clogged filter, not a faulty sensor.
How to Fix It
The fix is identical to the 'won't turn on' scenario, but it's even more critical. Remove the rear magnetic filter and clean it thoroughly under cold water. While it's off, also check the intake vents on the sides of the handle for dust bunnies. Let the filter dry for a full day before reassembling. The dryer needs unimpeded airflow to run continuously on high heat.
If That Didn't Work
If you're sure the filter is spotless and dry, you might be using it in a poorly ventilated area (like inside a small cabinet or drawer). Try using it in an open space. If it still trips, the thermal cut-out itself might be faulty, which requires service.
Heads Up
Running it on the highest heat setting (red) for very long periods, especially with a diffuser or concentrator attached that focuses heat back towards the body, can trigger this even with a clean filter. Try alternating between heat settings.