I had a mixing valve problem after 2 years. They have a tendency to get sediment on the sensor and not work. One good thing is if you soak them in white vinegar that takes care of the sediment. Obviously your situation is different. I bought another new one and installed it and kept the old one as a back up. This seems to be a common practice. If I were you I would do the same, because about the time you need it your really need it
. I also decided to get a water softener and a high quality filter to use to try and limit sediment issues.