I have a programmable Honeywell themstat . When I set it up to HOLD temperature at 76f , it works but later the setting falls to 71f buy it self. I have no indication of low battery. Could this be due to low batteries? ( my batteries are about a year old)
I have changed the batteries now.

Sounds like it is defaulting to another program. Does you have a regular program running? If you give me the model unumber I can show you how to clear the program out.

BTW most thermostat installation manual recommend replacing the battery every year so do that too.