The “Filter” icon will illuminate on the Zen Thermostat after 6 months of HVAC activity. This is to ensure that the filter is checked and replaced. If this action is ignored, the HVAC will not work effectively, causing the airflow from the HVAC unit to be disrupted which can lead to further HVAC issues. It is advised to change out the filter to maximize the efficiency of the HVAC over time.
For a more detailed description of the Filter icon and how to reset it please see the attachment below.