Photovoltaic (PV) modules installed in the field generate electrical power under different meteorological and operational conditions, therefore, maintenance of the modules is crucial for the longevity of the PV modules. Thermal Infrared (TIR) imaging is a widely used monitoring technique for quality checks of PV modules in plants. It is ideally conducted on operational PV modules under steady ambient conditions, however PV modules operate under dynamic climatic conditions which influence the overall operation of all solar cells and modules. The dynamic nature of thermal signatures was observed on TIR images when monocrystalline PV modules operated under varying electrical loads and irradiance. A change in operating conditions affected the level of current mismatch between cells since at high irradiance of about 1000 watts per square metre (W.m−2) and while operating close to short circuit current at reduced load, the PV cells generated a higher current which led to significant current mismatch. This resulted in several abnormally hot cells being identified on TIR images. Under lower irradiance and larger electrical loads, fewer hot cells were observed and cracked cells (identified through Electroluminescence (EL)) appeared as good cells due to minimal current mismatch. The effectiveness of TIR imaging to reveal underperforming defective cells as hot cells depends on the operating conditions and can mislead decision making when PV module maintenance is carried out. This work gives valuable information which can be of importance in improving the maintenance systems of PV modules when TIR imaging is conducted.