TH522 Digital Thermostat Installation Guide Addendum

Attention Installers

Installer must use the new wall plate shipped with the unit when replacing the following

thermostats:

TH5220D1003, TH5220D1029, TH6220D1002, TH6220D1028, RTH6350D1000,

RTH6450D1009, RTHL3550D1006, RCT8102A1016

Honeywell changed the design of these thermostats from using separate Aux & E terminals to a

single Aux/E terminal in 2012. At that time, a key/tab (see illustration below) was added to the

thermostat and wall plate which prevents assembly of a new thermostat with an old wall plate (pre

2012).

Removal of the key/tab and installation on an old wallplate may cause improper operation of the

HVAC system, will void the warranty of the thermostat, and could result in serious physical injury

or property damage.

Key/Tab circled: