The purpose of this study is to examine the process of conceptual change in which the heat concept has gone through in time and provide an analytical assessment. To this end, problem-based learning groups were formed with 13 sophomore university students. One of these students was selected and interviewed. The interviews were examined using the content analysis method, which is one of the qualitative analysis' methods. Grounded theory techniques were used to interpret the data. According to the results, the student had difficulties in distinguishing between heat and thermal energy. The student explained what heat is as "a type of energy stored in a matter" and how heat comes out as "a result of frictions which occur while particles of a matter collide with each other". It is seen that the opinions of the student are affected by common misconceptions such as "heat loss" or "the energy lost during friction turns into heat". The opinions of the student are disconnected pieces of information and her opinions change constantly throughout the process. At the end of the process, the student managed to differentiate the heat concept and thermal energy concept. In addition, she corrected her conception of heat in line with scientific theories.