Replace Only Batteries
You shouldn't need to replace your electronic thermostat regularly; however, thermostat batteries do require yearly replacement. Even if your thermostat's battery indicator isn't blinking, the experts at ESP Energy recommend replacing the battery once a year, before a period of heavy use, such as winter in the northern states or summer in the south.
Replace Broke or Inefficient Units
If your thermostat is more than 10 years old, it may start malfunctioning due to aging wiring or dust accumulation. Replace your thermostat if you notice indoor temperature changes indicating a malfunction. Another replacement scenario: an upgrade to a programmable thermostat, which will save you money by reducing your energy consumption.
Don't change your thermostat if it isn't malfunctioning; there isn't a set amount of years in an electronic thermostat's lifespan.