Honeywell RTH8500WF Wi-Fi Series Quick Start Manual page 4

1.2 Remove old thermostat
faceplate and leave wires
connected
1.2a Take a picture of the
wire connections for
later reference.
1.2b If no wire is connected
to a terminal labeled C
or no C terminal exists
on the old thermostat,
view the Alternate Wiring videos at
wifithermostat.com/videos
Important! C wire is required and is the
primary power source for your thermostat.
Without a C wire, your thermostat will not
power up.
If you have an older thermostat with a
sealed mercury tube, see warning page
for proper disposal instructions.
C
4
MCR33823