Battery Replacement - Honeywell RCT8100 Operating Manual

Battery replacement

Set the System switch to Off before removing the batteries.
Otherwise, the heating/cooling system might remain activated even
when batteries are removed.
Install two fresh AA batteries when the low-battery icon flashes on the
screen. The icon will flash for 120 days, then the thermostat will cut power to
the heating/cooling unit. The icon disappears once the batteries are
replaced.
Replace batteries once a year or before leaving home for more than a month.
After replacing the batteries, set the time and the day (see page 7). The other settings are
not erased when the thermostat is without power.
RCT8100 Programmable Thermostat
17 69-2337EF—01