Honeywell RTH4300B Guide D'installation page 18

Installation Guide
Mount thermostat and restore electrical power About your new thermostat
1. Align the 4 tabs on the wallplate
with corresponding slots on the
back of the thermostat, then push
gently until the thermostat snaps
into place.
2. Restore electrical power at the
heating/cooling system, or at the
fuse/circuit-breaker panel.
TIP: If wires interfere when you
try to mount the thermostat,
push excess wire back into the
wall opening.

Wallplate
Thermostat