Re: Honeywell CM921 Showing room temp at -24 degrees, How...
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)
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I believe what your experiencing is the 75 degrees is the hold temp position...the display then reverts back to the actual room temperature...it doesn't mean the set temperature changed back to 65 degrees. Try to reprogram the thermostat schedules, and try not to use the hold function...just the temporary hold. (which is bumping the programmed temperature up or down until the next programmed period)
You didn't include a model number, so it's hard to know for sure - but I'll take a stab at this one. Many of these t-stats have a programmable offset to reduce "hunting". This can be as little as 1 degree or more than 2 degrees.
This means if you set the offset to 1 degree and the room temperature to about 65 degrees, the furnace will heat the room until the t-stat registers a rising temperature of 66 degrees. The furnace shuts off and will not turn on again until the t-stat registers a falling temperature of 64 degrees. The average is 65 degrees, and prevents the furnace from starting and stopping numerous times instead of just once with the 1 degree offset.
You can further reduce the number of furnace start and stops by increasing the offset to 2 degrees. This would work like this when the t-stat is set to 65 degrees and the room is cool:
Room Temp Furnace 63 On 64 On 65On 66 On 67 On 68 Off
The room is now warm and heat or furnace is off. The room begins to cool like below:
67 Off 66 Off 65 Off 64 Off 63 Off 62 On
With a 1 degree offset, the room temperature varies +/-1 degree (about 2 degrees total). With a 2 degree offset, the temperature about varies +/ -2 degrees (about 4 degrees total).
Also, when the thermostat shut the heat off, the heat that was made is delivered to the space instead of wasted by sending outdoors - so the room will get a little warmer even though no fuel is being burned. The same holds true at the other end. When the t-stat turn heat on, fuel is burned, but there's little heat until the source has reached the optimum temperature and then the heat is delivered to the space.
I hope this helps & good luck! Pleas rate my reply - thanks!
It's either because the thermo sensor is faulty or the location is wrong. Try setting the temp one degree above room temp and see if that works, if it does it's a location issue. The thermo should be close to the centre of the house, not near an outlet or the RA vent & not in a breezeway or other heatsink, at approx 1.5m above floor level.
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
make sure it is not telling you room temp, some of the Honeywells, will display room temp over desired temp. check that, if it wont let you switch temp than buy a new one, if you dont have a heat pump a new cheap stat is around 20.00.