Heat is IR in normal circumstances. For thermal radiation you need reaaaalllyy high temperatures for UV thermal radiation. If we are talking heat related light source then we are talking about thermal radiation.
Another term we need is wavelenght. When you increase a photon's energy you give it more energy and wavelength is reduced, frequency is increased.
If a material gets hot is radiates more energetic photons. If you get it colder then photon energy is reduced.
Lets think like that; you can detect thermal radiation of an iron piece at 60 C with infrared. If you get it hotter; 150 degrees you will see that radiates with near infrared which is more energetic. When you heat is to 500 degrees you will see a yellow iron. This is because it radiates so energetic fotons that they are at visible spectrum. When you decrease the temperature to -270 degrees you will see that hermal energy is at microwave.(lower frequency, longer wavelength)
About UV; you need reaaly really high temperatures for UV that is not possible to emit in ordinary atmospheric conditions. But still, really hot gases can emit UV at minimum. Just enough to say they do. But it is really hard to detect.
When we see UV in other conditions?
As common; excited gases like excited ions of nitrogen. Taht can be seen with electric discharges or some high temperature and (rarely)chemical reactions in some rare occasions.
The catch is; thermal radiation is not like lasers. I will occur within a really wide spectrum and any source that emits peak thermal radiation at visual spectrum(really hot one) can radiate UV too but the probability is too low of these photons and they are practically not so usable at detection. If you want the peak at UV then you need 10000-15000C degrees .
For more information you can look for black body radiation.
