Honeywell CM921 User Manual

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 lashing.

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.