It is very rare for a device to be defective or become defective. In almost all cases, the reason for a device becoming less effective is due to the electrodes needing a good cleaning. Mineral deposits accumulate on the electrodes (metal plates) and need to be removed from time to time. There are many ways to clean these effectively. One of the easiest is to soak the electrodes in a half water/half vinegar solution overnight and then scrub them off the next day with a towel and then rinse. This almost always returns the device to its original efficacy level.