How do I access the Installer Setup (ISU) menu on the T6 Pro?
Press and hold the CENTER and arrow buttons simultaneously for approximately 3 seconds to enter the advanced menu. Press Select to enter ISU, then use the arrow buttons to change values and Select to confirm settings. Press the Home button when finished to save your settings and return to the Home screen.
From the official Honeywell T6 Pro TH6210U2001 Smart Thermostat manual, page 8
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