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Honeywell RTHL3550 Installation Guide

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RTH6400
 25 69-2697ES—03
Troubleshooting
SETUP
WIRING
ASSIST
ANCE
TR
OUBLESHOO
TING
Troubleshooting
If you have difficulty with your thermostat, please try the 
following suggestions.  
Most problems can be corrected quickly and easily.
Display is blank  •  Make sure fresh AA alkaline
batteries are correctly installed (see 
page 7).
Temperature  
settings do not 
change
Make sure heating and cooling 
temperatures are set to acceptable 
ranges:
•  Heat: 40° to 90 °F (4.5° to 32 °C).
•  Cool: 50° to 99 °F (10° to 37 °C).
Cannot change 
system setting 
to Cool
•  Check Function 1: System Type to 
make sure it is set to match your 
heating and cooling equipment (see 
page 13).
Fan does not  
turn on when  
heat is required
•  Check Function 3: Heating Fan 
Control to make sure it is set to 
match your heating equipment (see 
page 15).
Heating and 
cooling  
equipment  
running at the 
same time (or  
heat does not  
turn off)
•  Check Function 1: System Type to 
make sure it is set to match your 
heating and cooling equipment (see 
page 13).
•  Grasp and pull thermostat away from 
wallplate. Check to make sure bare 
wires are not touching each other 
(see page 6).