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Description  
The Honeywell CM921 is a ‘wireless’ programmable room thermostat designed to  
control you heating system efficiently, providing comfortable temperatures when you  
are at home and energy savings when you are away. With ‘wireless’ communication  
there is no need to provide a wired connection between the thermostat and boiler.  
The following instructions explain how to set up, program and operate your  
Honeywell CM921 Programmable Room Thermostat.  
Features  
Wireless connection to the boiler allows you to mount the Chronotherm in your  
room without decor disruption  
Armchair programming feature lets you program your Chronotherm while  
resting comfortably in your armchair  
Ergonomic User Interface features an ‘OK-button’ making the CM921 very  
easy to use so you always stay in control.  
LoT technology provides informative ‘on-screen’ feedback and operational  
assistance to the user.  
Extra Large LCD (Liquid Crystal Display) Screen with Backlight provides  
added user friendliness and clearer viewing – even in the dark.  
6 independent temperature levels per day lets you set any 6 temperatures you  
require (from 5 to 35°C) so you can enjoy economical comfort every day  
Holiday button saves energy by letting you reduce the temperature for 1 to 99  
days while you are away from home, resuming normal operation on your return.  
Automatic Summer/WinterTime Change will adjust the clock automatically for  
Daylight Saving Time’.  
Built-in Memory holds the user program indefinitely so that it is never lost –  
even if you remove the batteries.  
Optimum Start option is an advanced feature which ensures that the optimum  
temperature conditions are achieved at the required times (option set by your  
installer).  
Honeywell Control Systems Ltd.  
Arlington Business Park,  
Bracknell  
CM921 - User Guide  
1 day Wireless Programmable Room Thermostat  
with LoT technology  
Berkshire  
RG12 1EB  
Technical Help Desk: 08457 678999  
www.honeywelluk.com  
42011077-103 R1  
© 2006 Honeywell International Inc.  
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Controls Layout  
Contents  
GETTING STARTED WITH THE CM921  
1
2
3
4
5
6
STEP 1: Installing the Batteries......................................... 3  
STEP 2: Setting the Date and Time................................... 4  
STEP 3: Running the Built-In Heating Program ................ 4  
7
8
PROGRAMMING THE CM921  
The Built-in Heating Program............................................ 5  
Reviewing the Heating Program....................................... 5  
Modifying the Heating Program........................................ 5  
Disabling / Enabling Time Periods ................................... 7  
15  
DATE  
PROG  
AUTO  
MAN  
AUTOMANOFF  
9
OPERATING THE CM921  
OFF  
CM921  
1..6  
Choosing the Operating Mode ......................................... 8  
AUTO mode............................................................. 8  
MAN mode .............................................................. 8  
OFF mode................................................................ 8  
Adjusting the Time............................................................ 8  
During Normal Operation.................................................. 8  
Temperature Enquiry............................................... 8  
Temperature Override ............................................. 9  
Using the Special Functions............................................. 9  
HOLIDAY Function .................................................. 9  
10  
14  
13  
12  
11  
1
2
3
4
5
6
7
8
Day / Date Display  
Time Display  
9
Slider Switch  
FINE TUNING THE CM921  
10 Green OK Button  
Changing the User Parameters ...................................... 10  
Change the Time Format....................................... 11  
Reset the Built-in Program..................................... 11  
Summer / Winter Time Change ............................. 11  
LoT technology Display  
Heating On Indicator  
Battery Low Indicator  
Temperature Display  
11 Program Buttons  
12 Battery Compartment Lid  
13 Battery Compartment  
14 Holiday Function Button  
15 Time Change Buttons  
FAQ’s & TROUBLESHOOTING  
Trouble Shooting Guide .................................................. 12  
Frequently Asked Questions........................................... 14  
Temperature Change Buttons  
Temperature Enquiry Button  
WHAT IS A PROGRAMMABLE ROOM THERMOSTAT?  
An explanation for householders.................................... 17  
Manufactured for and on behalf of the Environment and Combustion Controls Division of Honeywell Technologies Sàrl, Ecublens, Route du Bois 37,  
Switzerland by its Authorised Representative Honeywell International Inc.  
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GETTING STARTED WITH THE CM921  
This section shows you how to setup and run the thermostat in 3 simple steps:  
STEP 1: Installing the Batteries  
Note: Please follow the instructions in this section only if the thermostat screen is  
blank (no symbols or digits are displayed). If the screen displays some information  
move on to STEP 2: Setting the Date and Time.  
To install the Batteries:  
a. Lift up the front cover of the thermostat  
to reveal the battery cover and product  
controls.  
b. Remove the battery cover by pressing  
down and sliding out.  
c. Insert the 2 x AA LR6 Alkaline Batteries  
supplied with the thermostat, ensuring  
the correct orientation (see ‘Controls  
Layout’ on page 2).  
d. After a short pause the thermostat will  
display information on the screen and  
is now ready for use.  
e. Replace the battery cover by sliding  
it ꢀrmly back into the front of the  
thermostat.  
PLEASE RESPECT YOUR ENVIRONMENT!  
Take care to dispose of used batteries carefully.  
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GETTING STARTED WITH THE CM921  
STEP 2: Setting the Date and Time  
To set the Date and Time:  
a. Move the slider switch to the DATE position. ‘SET THE DAY’ will be displayed on  
the screen and the day digits will be ꢁashing.  
DATE  
PROG  
AUTO  
MAN  
OFF  
b. Use the  
are pressed ‘DAY OK?’ will be displayed. Once the correct day is reached, press  
the green button to conꢀrm.  
or  
buttons to set the correct day. When either of these buttons  
c. Now the month digits will start ꢁashing and ‘SET THE MONTH’ will be displayed.  
Change the month and then the year using the or buttons, pressing the  
green button to save any changes made. (If an invalid date has been entered  
you will be returned to the start of the date setting mode).  
d. After setting a valid date, the time digits will begin ꢁashing and ‘SET THE TIME’  
will be displayed.  
e. Use the  
or  
buttons to set the correct time. Each press of the button will  
change the time by one minute and holding the button down will change the time  
slowly at ꢀrst and get progressively quicker. Once the correct time is set, press  
the green button to conꢀrm then ‘CHANGES SAVED’ will be displayed for a  
moment followed by ‘DATE COMPLETE’.  
Note: If the slider switch is moved at any time before ‘DATE COMPLETE’ is displayed  
the changes to the date and time will NOT be saved.  
STEP 3: Running the Built-in Heating Program  
The thermostat is now ready for operation. Move the slider switch to the AUTO  
position and the built-in heating program will start running. The built-in heating  
program has been designed to provide normal comfort requirements, but if you want  
to customise the default settings (as shown on the next page) please see the next  
section ‘PROGRAMMING THE CM921’.  
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pRoGRAMMING THE CM921  
The Built-in Heating Program  
The built-in heating program has 6 temperature level changes that can be set  
between 3.00am and 2.50am - allowing you to maintain the evening temperature  
after midnight. Each temperature level can be set between 5°C and 35°C, and  
adjusted in 0.5°C increments. The factory default program for heating is as follows:  
Period  
1
2
3
4
5
6
Time  
6:30  
21°C  
8:00  
18°C  
12:00  
21°C  
14:00  
18°C  
18:00  
21°C  
22:30  
16°C  
Temperature  
Reviewing the Heating Program  
To review or edit the heating program move the slider switch to the PROG position  
buttons to navigate between the 6 individual programming  
then use the  
periods.  
or  
Modifying the Heating Program  
To change the heating program:  
a. Set the slider switch to the PROG position, entering programming mode. ‘SET  
TIME 1’ will be displayed and the time settings for period 1 will be ꢁashing. The  
active period is highlighted by a ꢁashing square symbol around the numbers at  
the bottom of the screen.  
DATE  
PROG  
AUTO  
MAN  
OFF  
1
2 3 4 5 6  
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pRoGRAMMING THE CM921  
b. To adjust the period start time press the or buttons and ‘TIME 1 OK?’ will  
be displayed. Holding the button down will change the time quickly.  
Note: If you are pressing the or buttons and the display flashes the next  
change period, it means the next change will be pushed forward if you continue  
to press  
or  
buttons).  
c. Press the green button to conꢀrm the setting. ‘CHANGES SAVED’ is displayed  
for 1.5 seconds then ‘SET TEMP 1’ will be shown.  
Note: If the original time setting did not require adjustment press the green  
button to move on to step ‘d.’.  
d. The temperature setting for period 1 will now be ꢁashing. To adjust this press the  
or  
buttons and ‘TEMP 1 OK?’ will be displayed.  
e. Press the green button to conꢀrm the setting. ‘CHANGES SAVED’ will be  
displayed for a moment followed by ‘SET TIME 2’.  
f. The next time and temperature period will now be active. Adjust this by repeating  
steps b - e above until all 6 periods are set or move the slider switch to the AUTO  
position to run the program as set, at any time.  
g. After setting period 6 ‘CHANGES SAVED’ will be displayed as before.  
i. To exit the programming mode move the slider switch to the desired operating  
mode - AUTO, MAN or OFF. Note: To run the adjusted program select the AUTO  
mode.  
Note: If the unit is left in programming mode for more than 10 minutes without  
the slider being moved or any buttons pressed, ‘MOVE THE SLIDER’ will be  
displayed. Press a button to finish programming the thermostat or move the  
slider to select the desired operating mode.  
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pRoGRAMMING THE CM921  
Disabling / Enabling Time Periods  
The thermostat has 6 periods that can be programmed, but you may not need all of  
these switch points for your heating requirements. Therefore, any period from 2 to 6  
can be disabled or enabled as follows:  
To disable time periods:  
Go to the desired period ( 2 to 6 ) by moving the slider switch to the PROG  
position, then using the  
and  
buttons to navigate, ensuring the correct  
period is highlighted with the ꢁashing square symbol. Press and hold the  
button for at least 2 seconds and the display will indicate the period has been  
removed from the program.  
To enable time periods:  
Navigate to the disabled period by moving the slider switch to the PROG  
buttons. Once selected ‘DISABLED’ will be  
position, then using the  
and  
displayed. Press and hold the button for at least 2 seconds and ‘ENABLED’ will  
be displayed for a moment before returning to normal programming mode.  
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opERATING THE CM921  
Choosing the Operating Mode  
The thermostat can operate in three different modes: Automatic, Manual or Off. To  
set the operating mode move the slider switch to the desired position. The screen  
indicates which mode is currently active by displaying AUTO, MAN or OFF.  
AUTO (automatic) mode  
Automatic mode sets the thermostat to follow the temperature program (default  
or personalised). Operating the thermostat in this mode is the best way to  
maintain a high level of temperature comfort whilst maximising your energy  
savings.  
MAN (manual) mode  
Manual mode sets the thermostat to act as a simple thermostat with a ꢀxed  
setpoint throughout the day. The setpoint can be adjusted from 5°C to 35°C  
by using the  
or  
buttons. The thermostat will continue to maintain this  
temperature until another operating mode or temperature is selected.  
OFF mode  
Off mode sets the thermostat to control to a minimum temperature setting of 5°C  
(default) that acts as a frost protection measure for your home. This value can be  
adjusted by calling your installer.  
Adjusting the Time  
To adjust only the time during normal operation use the  
the time and press the green  
or  
button again to conꢀrm any changes.  
buttons to adjust  
During Normal Operation  
Temperature Enquiry  
In AUTO and MAN operating modes the thermostat will display the current room  
temperature, which is indicated by the text ‘ROOM TEMP’ displayed on the  
screen. To review the programmed ‘target’ temperature (the temperature which  
the thermostat is trying to maintain) press the button. This ‘target’ temperature  
value will be displayed ꢁashing and the text ‘TARGET TEMP’ will be shown for 5  
seconds before returning to the current room temperature value.  
In OFF operating mode the thermostat again displays the current room  
temperature, as above, but when the button is pressed the text ‘FROST TEMP’  
is displayed indicating the set value to protect your home. To modify this value  
please contact your installer.  
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opERATING THE CM921  
Temperature Override  
During normal operation (AUTO mode) the programmed temperature can be  
adjusted manually by pressing the or buttons. The ‘target‘ temperature  
will be displayed and ꢁash for 5 seconds – during this time the  
can be used to modify the set value.  
or buttons  
Note: This temperature override is cancelled at the next programmed  
temperature change.  
Using the Special Functions  
HOLIDAY Function  
The holiday function allows you to set a constant temperature (default = 10°C)  
for a speciꢀed number of days (from 1 - 99 days). This lets you save energy and  
related costs when you are away from home, but resumes normal operation on  
the day of your return.  
To set the Holiday function:  
a. Move the slider switch to the AUTO or MAN position.  
b. Press the  
button to display the holiday days counter and temperature  
.
setting, along with the holiday indicator  
c. The day after the current day will be selected and ‘RETURN DATE OK?’ will be  
displayed. Press the or time buttons to set the holiday time (1 – 99 days).  
Note: (The day and date will update according to the number of days  
selected).  
d. Press the green  
button to conꢀrm the setting.  
e. ‘CHANGES SAVED’ will be displayed for a moment followed by ‘TEMP OK?’.  
buttons to set the holiday temperature (5°C - 35°C)  
Press the  
or  
f. Press the green  
button to conꢀrm the setting. ‘HOLIDAY MODE’ will now  
be displayed on the screen until the return date is reached or the holiday  
mode is cancelled.  
The thermostat will now control to the new temperature for the set number of days  
that your home is vacant. At midnight the holiday counter will be reduced by one until  
the selected number of days have passed. The thermostat will then return to normal  
operation as set by the slider switch position (AUTO or MAN position). To cancel the  
HOLIDAY setting or to exit the function at any time press the  
or move the slider switch to a different position.  
button a second time  
9
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fINE TuNING THE CM921  
Changing the User Parameters  
The user mode allows you to modify some basic settings of the thermostat to meet  
your personal preferences. You can change the time display format (24hr or AM/PM),  
reset the heating program to the built-in settings and disable or enable the summer/  
winter time change feature.  
To change any of these user’s parameters:  
a. Move the slider switch to the OFF position, then press and hold the button for  
approximately 5 seconds. button for approximately 5 seconds.  
DATE  
OFF  
PROG  
AUTO  
MAN  
OFF  
CM921  
1..6  
b. Once entered the following information will be shown on the screen:  
1
0
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fINE TuNING THE CM921  
c. Now choose which one of the following parameters you would like to change:  
i) Change the time format  
CLOCK SELECT’ should be displayed on the screen - press the  
or  
buttons to select the preferred time format (12=AM/PM format, 24=24hr format)  
and the display will ꢁash, indicating a change has been made. To conꢀrm this  
change press the green  
button.  
ii) Reset the built-in program to the factory default  
Press the  
Press the  
time button once. The display will show ‘RESET PROGRAM’.  
or buttons to select the preferred setting (0=user program,  
=factory program) and the display will ꢁash, indicating a change has been  
1
made. To conꢀrm this change press the green button.  
iii) Enable or disable summer/winter time change  
Press the time button twice. The display will show ‘AUTO CHANGE’. Press  
the or buttons to select the preferred setting (0=disabled/Off, 1=enabled/  
On) and the display will ꢁash, indicating a change has been made. To conꢀrm  
this change press the green  
button.  
d. To exit the user mode move the slider switch to the AUTO, MAN or OFF  
position.  
1
1
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Troubleshooting Guide  
Symptom  
Possible Cause  
Remedy  
The thermostat has a blank LCD  
screen.  
Batteries not installed.  
Check to see if there are batteries in the battery  
compartment and the paper tab has been removed.  
Incorrect battery orientation. Check that the batteries have been installed in the  
correctorientation.  
Exhausted batteries.  
Replace with new batteries.  
Replace with new batteries.  
The thermostat shows a ꢁashing Batteries are exhausted and  
symbol on the LCD screen. need replacing.  
The thermostat’s LCD display  
shows a symbol but the  
heating does not switch on.  
The heating is not required  
at this moment.  
The heat demand is send to the HC60NG as a value  
between 0-100%. The HC60NG will adjust the boiler  
on time to meet this requirement. That is why the  
heating will be off sometimes even if the symbol is  
displayed. To check if RF system is communicating  
properly press the  
button to increase the set  
temperature a few degrees above the current  
temperature. The heating should come on after a few  
seconds.  
The thermostat shows a ꢁashing  
symbol on the LCD  
screen.  
Fault in thermostat  
Remove and re-insert the batteries in the thermostat.  
symbol does not clear itself in a few  
If the  
minutes call the installer.  
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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 ꢁashing.  
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.  
Call Installer.  
Temperature swings between  
too hot and too cold.  
The thermostat not set  
correctly for your system.  
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fAq’s & TRoublESHooTING  
How do I change the batteries on the CM921 when they run out?  
The thermostat constantly monitors the battery power level, which typically last for  
about 2 years before needing replaced. When the power is running low a ꢁashing  
symbol will be displayed on the screen. To change the batteries follow the steps in  
the above section (‘STEP 1: Installing the Batteries’ on page 3), replacing the used  
batteries with new ones in step c.  
Note: While changing the batteries your program settings will be stored but you may  
need to adjust the time and date settings to be correct.  
How do I set one temperature for the whole day?  
To operate as a simple thermostat with one temperature for a period of time, move  
the slider switch to the MAN position. Adjust the manual temperature by pressing the  
or  
buttons. This can be set anywhere from 5°C to 35°C in 0.5°C steps. The  
thermostat will continue to maintain this temperature until another operating mode is  
selected or the temperature is adjusted.  
What is Optimum Start?  
Optimum Start is a program which ensures that the optimum temperature conditions  
are achieved at the required times. This is an Energy Efꢀciency feature that adjusts  
the start time of your heating system depending upon how cold it is. For example,  
on cold days your heating system will be started earlier to ensure that your home is  
warm when you get up (at the target temperature) and on warmer days the heating  
system will be started later to save energy. So, if the Optimum Start Feature is used,  
then the time / temperature settings which are entered into the thermostat should  
be set to when you want to be warm by and not when you want the heating system  
to start.  
I want to use the table stand instead of wall mounted bracket. Where can I  
position the room unit?  
It is important to keep the room unit in a location where reliable RF communication  
was proven. Advise your installer where would you like to position the room unit and  
he will check if the RF communication is reliable in the selected location(s).  
Important: The Room Unit measures the temperature of the room where it is located.  
It is important that the placement of the Room Unit within the room is away from;  
draughts, direct sunlight and other heat sources. As this is a wireless device certain  
objects could interfere with the RF signal - Leave at least 30cm distance from any  
metal objects (including wall boxes) and at least 1 metre from any other electrical  
equipment eg. radio, TV, PC, etc.  
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fAq’s & TRoublESHooTING  
How do I remove the thermostat from the table stand or wall bracket?  
After programming is ꢀnished always replace the thermostat back on the wall holder  
or table stand.  
Wall bracket  
Table stand  
HC60NG Relay Box Controls Layout  
Push button and  
relay status LED’s  
What does it mean when the HC60NG relay box green LED is ON?  
Green LED indicates normal operation of the radio frequency system. When the  
green LED is ON the boiler is also ON. When the LED is OFF the boiler is OFF.  
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fAq’s & TRoublESHooTING  
Can I use my CM921 to control my air-conditioning system?  
Yes, if your system has been set up correctly you can use your thermostat to control  
the cooling. To switch the thermostat between heating and cooling modes press  
the  
(
or  
buttons together for 5 seconds in any of the product operating modes  
AUTO, MAN or OFF). The text ‘COOLING’ will be displayed for a moment on the  
screen to indicate the cooling operation is now active. The factory default program  
for cooling is speciꢀed in the table below, but this can be modiꢀed in the same way  
as the default heating program:  
periꢆd  
1
2
Time  
6:30  
24°C  
8:00  
28°C  
12:00  
24°C  
14:00  
28°C  
18:00  
24°C  
22:30  
24°C  
Temꢇeratꢈre  
If something happens to my heating system how can I check that the thermostat  
is working?  
Refer to the Troubleshooting Guide on page 15. If you still need assistance after this  
call your installer. The thermostat should only be opened or removed by a qualiꢀed  
professional to prevent possible injury from electric shock and/or damage to the  
product.  
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WHAT IS A pRoGRAMMAblE RooM THERMoSTAT?  
.
(
..an explanation for householders  
The following explanation applies to heating applications only)  
A programmable room thermostat is both a programmer and a room thermostat. A  
programmer allows you to set ‘On’ and ‘Off’ time periods to suit your own lifestyle.  
A room thermostat works by sensing the air temperature, switching on the heating  
when the air temperature falls below the thermostat setting, and switching it off once  
this set temperature has been reached.  
So, a programmable room thermostat lets you choose what times you want the  
heating to be on, and what temperature it should reach while it is on. It will allow you  
to select different temperatures in your home at different times of the day (and days  
of the week) to meet your particular needs.  
Turning a programmable room thermostat to a higher setting will not make the room  
heat up any faster. How quickly the room heats up depends on the design of the  
heating system, for example, the size of boiler and radiators.  
Neither does the setting affect how quickly the room cools down. Turning a  
programmable room thermostat to a lower setting will result in the room being  
controlled at a lower temperature, and saves energy.  
The way to set and use your programmable room thermostat is to ꢀnd the lowest  
temperature settings that you are comfortable with at the different times you have  
chosen, and then leave it alone to do its job. The best way to do this is to set low  
temperatures ꢀrst, say 18°C, and then turn them up by one degree each day until  
you are comfortable with the temperatures. You won’t have to adjust the thermostat  
further. Any adjustments above these settings will waste energy and cost you more  
money.  
If your heating system is a boiler with radiators, there will usually be only one  
programmable room thermostat to control the whole house. But you can have different  
temperatures in individual rooms by installing thermostatic radiator valves (TRVs) on  
individual radiators. If you don’t have TRVs, you should choose a temperature that  
is reasonable for the whole house. If you do have TRVs, you can choose a slightly  
higher setting to make sure that even the coldest room is comfortable, then prevent  
any overheating in other rooms by adjusting the TRVs.  
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WHAT IS A pRoGRAMMAblE RooM THERMoSTAT?  
The time on the programmer must be correct. Some types have to be adjusted  
in spring and autumn at the changes between Greenwich Mean Time and British  
Summer Time.  
You may be able to temporarily adjust the heating programme, for example,  
‘Override’, ‘Advance’ or ‘Boost’. These are explained in the manufacturer’s  
instructions.  
Programmable room thermostats need a free ꢁow of air to sense the temperature, so  
they must not be covered by curtains or blocked by furniture. Nearby electric ꢀres,  
televisions, wall or table lamps may prevent the thermostat from working properly.  
4
2011077-103 R1