When using any heat-styling tool on your hair, you should test the temperature first:
Get a paper towel and moisten it until it's damp. Press the tissue paper
between the heating plates of your flat iron and hold for a few seconds. Discoloration, smoking and sizzling of the paper, would be an indication that the iron is too hot.
For hot combs, place the comb on a dry piece of paper and leave it for a few seconds. An imprint of the comb is normal but any discoloration or burning would also signal the need to rest the comb or turn down your heating oven.