If the thermostat is already mounted on the wall, remove the thermostat
by placing your thumb between the thermostat and wallplate and
pulling the thermostat up and away as shown.
When the batteries are running low, a REPL BAT message flashes for one
to two months before the batteries run out completely. Replace the
batteries as soon as possible once the message flashes.
Although the thermostat has a low battery indicator, replace the
batteries once per year to prevent leakage and to prevent the
thermostat and heating/cooling system from shutting down due
to lack of battery power in the thermostat.
If you insert new batteries within 20 to 30 seconds of removing the old
batteries, the system retains the current time and day. If the display is
blank, the batteries are dead or installed incorrectly. You must reset the time and day. Refer to Set the Clock for
As a precaution when leaving home for longer than a month, change batteries before leaving to prevent
the system from shutting down due to lack of power. Always use fresh alkaline batteries. Nonalkaline
batteries do not last as long. They also can leak, causing damage to the thermostat and the wall surface.
Honeywell recommends Energizer® batteries.
STEP 6. MOUNT THE THERMOSTAT
ENGAGE TABS AT TOP
EDGE OF CASE