Okay. This evening, after many, many months of not having to even pay attention to it, my Zen thermostat did something really weird. I don't know if there was some sort of power surge or if something from one of the X-class solar flares we have had recently, or something entirely random happened.
I noticed that the house was getting warm. It should not have been as it should have been cooling. Instead, the setpoints had changed so that instead of the usual cool setpoint of 76, it was 92. Instead of the heating setpoint being at 72, it was at 85. The furnace was running. Since it was time for the night temperatures of 74 cooling and 68 heating to set in, I made the changes. However, they kept reverting. I removed the thermostat from the wall and changed the batteries, even though I do use a C wire. The new batteries did not help. Finally, I manually switched from auto to cool. It still was not cooling although the fan was running. Since the fan was on auto, it should not have been.
I went to the main panel and turned the furnace/AC off. I was not sure if it would help. Initially it did not seem to so I got the KonoZ that I purchased a while ago to get ready to change the thermostat. I had to shut down the system so another trip out to the panel to turn the breaker off. I removed the Zen from the wall and scrolled though some of the menu information. Just on a whim, I put it back on the wall and went out and turned the breaker back on. The system started working correctly again.
I don't know what did the trick unless it was threatening the Zen with being replaced by the KonoZ. Hopefully, this was just a one-time glitch and I will wind up keeping the KonoZ as a backup. After all, it worked this time. 
