The contacts of a thermal switch are the most possible parts to fail. Once the contacts failed to open, the thermal switch would be malfunctioned. There are several possible reasons to cause this failure.
1. Working current is more than the rated current. For example, the rated current is 5A. If you use this thermal switch to a 10A circuit, it would cause the contacts fail to action. Meanwhile, the life cycles would be much less than the rated value also.
2. The thermal switch suffered abnormal pressure. The imposed pressure would make the case of thermal switch distorted. The action room of bimetal would be narrowed. Then, there is no enough space or strength for the bimetal to trip off. The contacts would keep in close status and fail to open.
3. The contact resistance is too big. If so, every cycle of action would generate too much heat. Gradually, the contacts of thermal switch will be burned and failed to action.
