How do I access the Installer Setup (ISU) to configure advanced settings?
Press and hold the CENTER and arrow buttons simultaneously for approximately 3 seconds to enter the advanced menu. Press Select to enter ISU, then press Select again to cycle through the setup options. Use the arrow buttons to change values, press Select to confirm, or press Back to ignore changes, and press Home when finished to save your settings. (Page 8)
From the official Honeywell T6 Pro TH6210U2001 Smart Thermostat manual, page 8
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