Sorry, A second thermostat fixed the problem when I saw this situation before. The Children figured out how to "fix" the thermostat, so we put a new thermostat in another room and hid it behind some shelves. The thermostat in my home is actually in my bedroom.
Leave the old thermostat on and keep the batteries fresh.
That's all I've got. A thermostat with password security may exist, but I don't know where to get one.
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