Can an old thermostat be inaccurate?

Yes, an aging residential wall thermostat can certainly become inaccurate over time as its internal electronic components degrade, dust accumulates around sensors, and calibration drifts. While digital and smart thermostats have no moving parts to wear out mechanically, their internal thermistors, microprocessors, and solder joints are exposed to constant thermal expansion and contraction over a ten-to-fifteen-year lifespan, which can skew temperature readings by several degrees. This inaccuracy causes your HVAC system to turn on too early or run too long, resulting in uncomfortable indoor climate swings. You can troubleshoot by cleaning dust out of the housing or adjusting the temperature calibration offset in the settings menu. You can verify that an old thermostat needs replacement when calibration fails to correct persistent temperature discrepancies.