The heating system check assesses the overall efficiency of a heating system (in accordance with DIN EN 15378). In addition to flue gas loss, the measuring device—with the appropriate option—can also record heat losses via the boiler surface and the flue gas system and calculate them for the heating system check. Using a total of 10 assessment criteria, which cover not only heat generation but also heat distribution and heat transfer, the system condition and potential for improvement can be identified quickly and easily.