Press and release the MENU button and use the arrows to scroll to Installer settings then press and release the SELECT button. Use the arrow to scroll to SERVICE MONITOR then press and release the SELECT button. Use the arrows to scroll to FILTER MONITOR then press and release the SELECT button. You may use the arrows to set the timer from 0-980 hours in 20 hour increments. Press the SELECT button and then press the back button to return to the main scren or just leave the thermostat and it will return itself.