Honeywell CT8775A - Manual (Page 5)

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Replacing a thermostat that is connected to three wires on a warm air heating only system
If you are replacing a thermostat that is connected to three wires on a warm air heating only system and could turn the
fan on by setting the thermostat fan switch to ON, the CT8775C Thermostat will work with your system. Continue with
the installation at Step 4. If you purchased a CT8775A thermostat, return the product to the place of purchase. The
CT8775A thermostat is not compatible with this application.
Replacing a thermostat that is connected to three wires on a zoned hot water heating system
If you are replacing a thermostat that is connected to three wires on a zoned hot water heating system, the
CT8775A,C thermostats will only work if an isolation relay is installed. For details, call your local heating and/or cooling
contractor.
STEP 4. LABEL THERMOSTAT WIRES
❑ Disconnect the wires from the old thermostat. As you disconnect each wire, attach
the enclosed labels with the old terminal designation. Wrap the wires around a
pencil as shown to keep them from falling back into the wall.
STEP 5. SEPARATE WALLPLATE FROM
THERMOSTAT
❑ Remove cover from thermostat. Separate the wallplate from the
thermostat by placing your thumb on the top between the
wallplate and the thermostat and pulling the thermostat away from
the wallplate. See the illustration at the right.
STEP 6. MOUNT DECORATOR COVER PLATE
AND THERMOSTAT WALLPLATE
❑ The decorator cover plate and wallplate can be mounted directly
on the wall or onto an electrical box.
❑ To mount directly to the wall, see Fig. 1.
❑ To mount onto an electrical box, see Fig. 2.
WIRES THROUGH
WALL OPENING
M5136
WALL PLATE
THERMOSTAT
COVER REMOVED
M19492