Hello, how can I help you today? The most likely cause of that is going to be your temperature sensor , or your thermistor as it's called for that model. This picks up the water temperature and relays it to the circuit board to tell it when to turn on and off. If the sensor has failed and is reading the wrong temperature, it will cause the same issue you're experiencing. The part number you'd need is XXXXX-XXXXX and they only run around fifty dollars or so and are pretty easy to change yourself if that's something you want to do. If after changing the thermistor, it's still doing the same thing, then you're down to a bad board at that point, but it's much more likely to be the thermistor than it is the board, that's a common part to go bad on all brands of heaters. It will be threaded right in to the side of the water manifold where your plumbing comes in and out of the heater.