The use of thermal fuses are a safety feature that is very important. They are thermally coupled to the protection elements (metal oxide varistors) and have the function of disconnecting the power lines in case of thermal overload. In the performance of their protective function, varistors can age and become pre-damaged. As a result, leakage currents of the order of several amperes can flow through these protective elements. The resulting heating can cause these elements to glow without a line protection fuse noticing, which can be a major safety hazard. Replacing a thermal fuse would not change this situation; the protective elements would have to be replaced as well. This should not be carried out by an electrotechnical layman.
