Honeywell CT3550 - Manual (Page 7)

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Replacing a Thermostat that has Three Wires
If you have three wires for a heating only system and can operate the fan using the fan ON switch this thermostat
works with your system. However, some hot water (zoned) heating systems also have three wires. Your thermostat will
work only if you install an isolating relay on these systems. For details, call your local heating and/or cooling
contractor.
STEP 3. MOUNT THERMOSTAT WALLPLATE
❑ Separate the wallplate from the thermostat by placing your thumb or fingers between
the bottom of the wallplate and the thermostat, and pulling the wallplate up and away
from the thermostat. See illustration at right.
❑ Position the wallplate on the wall. Level the wallplate for appearance if desired. Use a
pencil to mark the two mounting holes that best fit the application.
❑ Remove the wallplate from the wall. Drill two 3/16 in. holes in wall (if drywall) as shown.
For materials such as plaster or wood, drill 7/32 in. holes where marked. Gently, tap the
(provided) anchors into the drilled holes until they are flush with the wall.
❑ Reposition the wallplate over the holes. Pull the wires through the wiring opening.
Loosely insert mounting screws into each of the holes.
❑ Level the wallplate if desired. Thermostat functions
properly when not level.
❑ Tighten mounting screws.
M16427
WIRES
THROUGH WALL
WALL
MOUNTING
HOLES
M15044
MOUNTING
SCREWS
WALL
ANCHORS (2)