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CT3451 PROGRAMMABLE THERMOSTAT
69-1620—1 2
2 REMOVE OLD THERMOSTAT
❑ Test to be sure your heating and air conditioning
systems (where applicable) are working correctly. If
not, contact your local heating/air conditioning dealer.
To avoid compressor damage, do not operate the
cooling system when outdoor temperature is below
50°F (10°C).
Not compatible with any 120/240 volt circuit.
a
Compatible with 2-wire Honeywell zone valves. Isolating relay required for zone valves that have a 3-wire thermostat
connection.
CAUTION
Equipment Damage Hazard.
Handling wires during installation can
damage equipment.
Disconnect power at furnace or main breaker/
fuse box before beginning installation.
❑ Carefully unpack your new thermostat and wallplate
and save package of screws, instructions and receipt.
❑ Remove the cover from the old thermostat. If it does
not snap off when pulled firmly from the bottom, check
for screw that locks on the cover.
❑ Loosen screws holding thermostat to subbase,
wallplate or wall and lift away.
❑ Disconnect wires from old thermostat or subbase. As
you disconnect each wire, use the wiring labels
(enclosed) to label each wire with the old terminal
designation. If there are only two wires, they do not
require labeling. Wrap wires around a pencil to keep
them from falling back into the wall as shown in Fig. 2.
Fig. 2. Wrapping wires around pencil.
Replacing Clock WIth C or C1 Clock
Terminals
If you are replacing a Honeywell Chronotherm®
Thermostat, you may find one or two wires that go to the
C or C1 clock terminals on the Chronotherm®
Thermostat wiring wallplate. Do not allow them to touch,
or you can damage your transformer. Disconnect the
wires and wrap them separately using electrical tape; do
not wrap them together. Do not place the wires where
they can interfere with the new thermostat operation.
Record the colors and terminal designation labels of the
remaining wires.
Six or More Thermostat Wires
If there are six or more wires connected to the thermostat
(excluding clock wires attached to terminals), you
probably have a variation of a multistage heat pump or
other multistage system. The thermostat is not
compatible with these systems, so return the product to
your retailer. If you want information about which
programmable thermostats work with your system, visit
our Web site at www.honeywell.com/yourhome or call the
customer information line at 1-800-468-1502.
Three Thermostat Wires
If you have three wires for heating only and can operate
the fan using the Fan On switch, this thermostat works
with your system. However, some hot water (zoned)
heating systems have three thermostat wires. The
thermostat works only if a contractor installs an isolating
relay on these systems. For details, contact a local
heating/cooling contractor.
Table 1. Compatibility Chart.
System Type Compatible With CT3451
Gas—standing pilot Yes
Gas—electronic ignition Yes
Gas-fired boilers
Yes
a
Gas—750 millivolt Yes
Oil-fired boilers
Yes
a
Oil-fired furnace Yes
Electric furnace Yes
Electric air conditioning Yes
Single stage heat pumps (no backup or auxiliary heat) Yes
Baseboard electric (120/240 line volt) No
Multistage heat pumps/multistage equipment No
WIRES THROUG
H
WALL OPENING
M5136