I have a NUC6CAY which runs with all cores at about 57°C. It is in a cool(ish) room, ambient around 16°C so not excessive heat from its environment.
I power on and leave it idling with nothing other than Windows 10 - there are no other applications apart from the small app which I am using to obtain the temperatures so to all intents and purposes it isn't doing a great deal but does seem rather hot.
I have removed the motherboard (and broke a RAM clip in the process) to see if the fans and channels were blocked but they weren't.
I'm quite concerned as the temperature is likely to rise when actually working especially as I was planning on having it constantly on running.
What are the thermal limits of these NUCs? If it overheats, are there any thermal safe guards to prevent fire hazards?
The operating temperature range differs from component to component.
The processor and chipset (PCH) will operate at temperatures between 0 and 100c. At and above 100c, you are going to see the processor throttling performance to protect itself and, if temperatures continues to rise, a thermal trip will occur and power will be shut off. So, what to consider concerning? Any sustained temperatures at or below, say, 90c is perfectly fine. Occasional spikes above 90c are no issue either. Sustained temperatures above 90c should be where it should start to concern you.
Memory and internal drives can typically operate at temperatures between 0 and 80c. Most SSDs will throttle their performance to protect themselves if temperatures go above 80c.
Hope this helps,