Excess biogenic amines can cause sensations of flushing and heat.

Serotonin and histamine are two that may be elevated for some people. Carcinoid syndrome is one ...often hard to diagnose until it gets severe.
http://www.medicinenet.com/carcinoid...me/article.htm

Hidden tumors (mostly commonly lung) secrete biogenic amines sometimes.

You can test the histamine possibility by taking Benadryl and Zantac. Both block histamine receptors. They are often used in allergic food reactions. If they help, that would point to histamine.

Check your diet for monosodium glutamate, as this food additive which is very common, can wreak all kinds of havoc in people.

This is a link to histamine releasing foods. Some people eat alot of them and their bodies react by releasing histamine excessively:
http://www.michiganallergy.com/food_and_histamine.shtml

I really think the solanine alkaloid in potatoes is problematic for some people too:
http://www.michaellebowitzdc.com/html/Solanine.html

There is also a condition called erythromelalgia, which causes flushing. Many find using magnesium either topically or by supplement helps.
http://medicationsense.com/erythromelalgia.html

This is my magnesium thread:
http://neurotalk.psychcentral.com/thread1138.html

Do not purchase magnesium oxide, as this form is not absorbed and will not help those who need magnesium supplements.

People with elevated thyroid functions often feel hot.
So get that checked if you haven't done so already.

Are you taking any SSRI or SNRI drugs for depression or pain?
These can cause flushing too.