I have the same problem where my honeywell cm921 room thermostat never turns off the central heating. If I set my off temp really low will this solve the problem, but if its really low does this become the target temp and my heating will always be cold? My current settings are the default factory setting. Thank you for your help Paul

The problem you're experiencing with your heating system could be caused by a malfunctioning thermostat. The thermostat may not be properly calibrated, or it could be faulty, causing it to incorrectly read the temperature and turn on the heating when it's not needed. It could also be caused by a problem with the heating system itself, such as a malfunctioning valve or a blocked duct.

you need to go into the setup menu and configure your tstat for what type of heating you have.

If you need further help, reach me via phone at https://www.6ya.com/expert/thomas_092728000e6acb79

Probably not. There are replacement models available.
The T6661B programmable room thermostat is also known as CM61.
CM61 1 day wireless programmable thermostat is replaced by CM921.
CM61 1 day wired programmable thermostat is replaced by CM901.

Centigrade?

Hello Try RAISING the temp setpoint in COOL mode,sometimes there is a deadband so unit will not conflict.

HONEYWELL WEBSITE:
Go to honeywell.com
Under red welcome sign
Bottom red highlighted box literature/image search
Type in thermostat model number
Click on arrow to right
Then click on the PDF files owners manual / installation instructions
If you can’t find what you want, the bottom left and bottom of web
Page, they have homeowners assistance and Home products to get the help you need.

if you have a programable tstat you need to go through the settings for each day and time. usually the buttton will say prgm or program sometimes it will be set try to get into the settings menue and then you can adjust times

Turn up your outside thermostat in the outside unit.
You should have about 3 degrees difference in one stage to the next. So I would change the thermosat with one that has three stages of heat.

Heya this is a manufacturing fault from honeywell them selves when it comes up -24 basically it needs to be replaced there is no way around in if you get in touch with honeywell they are generally good about it also if you provide them with the date code and model code they will be greatfull as it seems they have sent out a "bad batch". you locate this by:

A) Move the slide in to the off position
B) Press and hold i for 5 seconds
C) Unit will enter settings mode
D) Press and hold the i button and the + and ¿ button together
E) The unit will hold the relay on for 5 minutes and you can view by pressing the down arrow twice for model id/date code (ww/yy)

I hope this helps

Remember the is a time and temperature controller if you want to use as an ON/OFF controller please ensure you OFF times are set to LOW temperatures for example at 8:00am I want the boiler firing to 21°C at 10:00 I want the boiler to go OFF at 5°C so ensure all so called OFF times are set to LOW temperatures.