A solid understanding of students' conceptions in thermal physics is absolutely necessary for successful development of instruction and for promoting understanding of and enthusiasm for the subject. This study reports on student understanding for a range of thermal topics. The sample included first and second year university students studying physics and the tool was a short, 15 question, concept inventory-like 'Diagnostic Survey' administered at the beginning of first semester 2009 at the University of *****. The results indicate that some thermal physics misconceptions exist for a large proportion of tertiary level students. More specifically, basic concepts, such as heat transfer, appear to be systematically misunderstood by the more novice student. For Australian tertiary instructors, our preliminary diagnostic could provide information about student's abilities in thermal physics and, consequently, why they experience difficulty understanding similarly structured fundamental processes in other physics topics. The subjects covered in our diagnostic are considered a foundation of any thermal physics course and are present in many further science related courses. Thermal topics such as atmospheric thermodynamics and climate change thermodynamics have lately appeared the popular headlines, strengthening the justification for at least a basic understanding of such topics from students studying physics at university.