Has anyone heard of a programmable thermostat turning itself on? We have two Honeywell programmable thermostats in the house, one upstairs and one downstairs. Recently we have seen that they are turning themselves on to cooling mode from an 'off' state. All the schedules are still in place, but when they turn themselves on, they go to 65 degrees which is not a setting in any of the schedules.

I had a Honeywell programmable thermostat that was close to 10 years old. At the end of last summer while I was away, it turned itself on to the heat mode. I had to turn off the breaker to my heat pump to shut it down. I replaced with a new thermostat and the problem went away. It seems strange that both of your thermostats would malfunction at the same time. Unless you get a more concise answer from one of the HVAC experts, you might consider replacing one thermostat to see if that cures half the problem. Good luck.

Unless something has changed with your wiring/programing your ststa have bit the dust. It could have been a electrical surge that caused the problem with both. I do find it strange that they are both bad at the same time. Have you tried to reprogram? If they stay on no matter what you do it is the relays in the stats that have welded shut.
The new ones are more accurate as long as you get Honeywell. Usually 1/2 of 1 degree difference from setting some other brands can be up to 3 degrees up or down from setting.

I have seen two go bad at the same time, a few times but as hvac1000 said it was due to a power surge. The old mercury bulb was accurate + or - 4 degrees, all digital stat now should be + or - 1 degree. I would think about having them changed out. The operation of them will only get worse and more erratic.