Do-It Yourself Models
For 24 Vac, Heat-Only Systems
The CT40A Heating Thermostat replaces most 24 Vac,
2-wire heating system thermostats. It is suitable only for
gas or oil heating systems or for electric heating systems
that control the fan. The CT40A is not suitable for air
conditioning, heating/air conditioning, heat pump or line
If this control is replacing a control that contains
mercury in a sealed tube, do not place your old
control in the trash.
Contact your local waste management authority
for instructions regarding recycling and the
proper disposal of an old control containing
mercury in a sealed tube.
® U.S. Registered Trademark
Copyright © 2002 Honeywell •
CT40A Heating Thermostat
• All Rights Reserved
1 Prepare for Installation
To correctly install your Honeywell thermostat, follow
these step-by-step instructions. It is recommended that
as you read, understand and complete each step, you
check it off. If you are unsure about wiring procedures, be
sure to call a qualified service technician for assistance.
Check thermostat suitability for your home system by
reviewing the introductory paragraph.
Assemble tools required as shown in Fig. 1.
WIRE CUTTER/STRIPPER OR SHARP
KNIFE, IF NEEDED TO STRIP WIRES
SPIRIT LEVEL, IF NEEDED TO LEVEL
THERMOSTAT FOR APPEARANCE
Fig. 1. Assemble required tools.
Be sure your heating system is working, especially if
inoperative for a length of time. If the heating system
does not work, contact your local heating dealer for
Carefully unpack your new thermostat. Discard the
cardboard insert protecting the snap switch contacts.
Save the package of screws and all instruction pages.
2 Review Thermostat Features
See Fig. 2 for thermostat parts.
HAND OR POWER
DRILL WITH 3/16 INCH
DRILL BIT, IF NEEDED TO
DRILL HOLES IN WALL