Heating device using photodetector to detect temperature and method for protecting the same

A heating device comprising:

• a housing provided at an inside thereof with a flow channel for flow of working fluid;
• an electric heater disposed in the flow channel and being capable of emitting lights;
• an optical rod having a transparent body, a first end portion, and a second end portion opposite to the first end portion and located inside the housing;
• a light guider provided at the second end portion of the optical rod and facing the electric heater for receiving the lights emitted by the electric heater and guiding the lights toward the first end portion of the optical rod;
• and
• a photodetector located adjacent to the first end portion of the optical rod and facing the second end portion of the optical rod for indirectly receiving the lights emitted by the electric heater to the light guider through the transparent body of the optical rod and generating a detection signal corresponding to a temperature of electric heater.