In this study, thermoelectric generator (TEG) adaptation in a condensing combi boiler was investigated. The first part of the study comprises experimental analysis, performance tests of a commercially available TEG, and efficiency tests of a condensing combi boiler without TEG adaptation. In the second part of the study, a numerical analysis was carried out to determine the locations of TEGs inside the heat cell. According to the results of the performance tests, approximately 16V open circuit voltage was generated under 201 degrees C temperature difference. The electrical efficiency of the tested TEG is calculated to be 4.5%. Natural gas was used as fuel in the efficiency tests of the condensing combi boiler and the thermal efficiency was calculated to be 92.3% for 40-60 degrees C water supply and return temperatures. Numerical study showed that the highest temperature difference could be obtained at the upper side of the heat cell with a value of 270 degrees C. The hot side of the TEG module was heated from the inner surface of the heat cell via conduction through the wall, and the water channel was used as the heat sink. Therefore, TEGs were located inside the water channel of the heat cell, with a modification process on the heat cell itself. The performance tests and numerical results show that it is possible to integrate TEGs into the heat cell and decrease the electricity consumption or use combi boilers without an electricity network connection with a properly designed TEG integrated heat cell.