Honeywell CM921 Thermostat User Manual


 
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Symptom Possible Cause Remedy
The thermostat’s LCD display
works but the heating does not
switch on (HC60NG LEDs are off
or green one is on).
No power to heating system. Check that there is power to the heating system.
Program does not call for
heat.
Move the slider switch to MAN and press
or to
increase the temperature a few degrees above the
current room temperature. The heating should come
on after a few seconds.
Wrong electrical connection. Call electrical installer to check the boiler and
HC60NG power supply as well as the connection
between the boiler and the HC60NG.
The red LED on the HC60NG is
constantly on or flashing.
RF communication lost due
to the wrong location of the
thermostat.
Hook the
thermostat
back on the wall bracket or
replace the
thermostat
on the table stand in the
position where RF communication was reliable.
RF communication fault.
Call installer.
NOTE: You can control the boiler manually when the RF
communication is lost: Press the HC60NG push button
to switch the boiler on and off. When the green LED is
on – the boiler is on.
Heating switches ON or OFF too
slowly or quickly.
The thermostat not set
correctly for your system.
Call Installer.
Temperature swings between
too hot and too cold.
The thermostat not set
correctly for your system.
Call Installer.