About two weeks ago the water was abnormally hot one day. The next morning the water was cold. I determined that the lower element was burned out and both high limit reset buttons needed to be reset. I replaced both elements at that time as there was a build-up on both and I figured that since I was into the job, and elements are cheap, that it was a reasonable thing to do. The hot water heater has worked fine for the past two weeks at about 120 degrees.Today the water was very hot–about 170 degrees at the nearest tap. I shut the hot water heater off so as to not burn out the elements. I suspect that one or both of the thermostats is bad.I have some electrical test equipment (inherited from my father-in-law) but am not clear on how to use the meters to test the thermostats (or if its even possible). How do I test the thermostats? What else could cause this problem?Thanks,John