How do I remove the thermostat cover to change the battery?

Yes it has 3 AAA batteries.
Pull it straight off the wall. Look at the back of the thermostat and replace the three batteries.

Link to manual..
http://www.lennox.com/pdfs/manuals/Lennox_Elite_Touchscreen_Manual.pdf

if this is the bypass model there is a screw at the bottom of the cover that needs to be loosened. then the cover will flip up to expose the tray that holds the pad. take the tray out and squeeze the tabs on the black filler port to remove it. once the tray is out the top distribution tray can be removed by pulling the lower part off the tabs on the distribution tray. once they are apart remove old pad and wash both parts very well. You may need to scrub off the calcium build up or soak it in CLR to loosen scale. Once you have done this put the new pad in and clip the black filler port back on and test the humidifier.

first , make sure thermostat is level on the wall. If o.k. try adjusting the anticipator at the thermostat. remove cover and you should see same as in picture. Move arm away from longer slightly, and try it a few times, each time before going more. If that doesn't help, it may be time for a new thermostat.

Open the front panel, opens from the top, hinge at the bottom. You will see 2 Philips screws at the bottom at the "hinge" part. Unscrew them. Pull the thermostat from the wall by pulling off the top part. You need 3 AA batteries. You have 20-30 sec to change the battery without re-setting the program, so be prepared and have batteries handy. Make sure your + and - are in correct order- have a flashlight handy to see well. If you done it in time- you all set, if you are a bit late prepare to re-program according to your liking. You can re-program it while it is away from the wall, sitting in your chair! Instructions are on the inside panel, which you open All the best!

It would appear to me that you have lost the 24 volt power supply to the thermostat. In referencing the manuals for this thermostat, available @ www.honeywell.com, I've found that when the thermostat is not connected to the wall plate (plate mounted on the wall, that the thermostat either snaps or screws into), it will display the -AC. This being said, either the thermostat is loose on the wall currently, or your 24 volt transformer has died. Hope this helps.

Thermostat problem; Honeywell chronotherm lll ' Low Batt. indicator Keeps blinking after Batteries replace. I chk'd batt. with elect. volt ntr. Was told to pull batt. and change ends with them , letthem stay reversed for 5-10 sec. then put them back in right order,and replace thermostat. No success!
Anyone have any answers

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

No. when you remove the front cover it will automatically disconnect the power supply. Try changing the water panel and cleaning out the orifice and filter screens located in the water lines connected to the solenoid valve.

Hello Genna,
I am not a furnace guy but I may be able to give you a few ideas of things to diagnose the problem and get it resolved. First off, I assume you have a thermostat that you use to to turn your heat on. If it is a generic ( meaning : non programmable model) then you should be able to try this simple test. Remove the cover ( typically they snap on) around the thermostat so you can see the control mechanism inside. You should see few skinny wires ( similar to those used on a telephone wire) solid copper in various colors.. When you rotate the dial on your thermostat to call for heat, there is a small glass vial that has a drop of mercury ( which is electrically conductive) in it that makes contact and shorts two control wires together ad that is what calls for heat on your furnace. When the temp inside the room where the thermostat is reaches the tempertaure you requested, the bimetal mechanism either contracts or expands to reposition that glass vial to shift the mercury off the contacts and your furnace shuts off... That is the basics behind how your thermostat and furnace work ( generally speaking) If you can identify the two wires inside the thermosat that are shorted together when that vial of mercury shorts them inside it.. you can temproarily unhook them ( they are low voltage.. normally 24 Volts or less) so no worries about getting ashock or anything.. and short them together for a minute or two.. by doing that... your furnace should turn on and heat should flow.... Once you start your furnace this way.. unhook these two wires and your furnace should shut down .. It may take a minute or two ( depending on the control for it) If it doesn't..then your problem is on the furnace side and you may need to get the furnace control system serviced or replaced.. if it does shut down, then your problem is your thermostat and thats a simple replacement.. Also.. make sure the thermostat was properly leveled on its base.. The position of the thermostat ( meaning level) will dictate when that mercury makes contact and your furnace switches on.. OK..I tried to explain the works of this to you but here is a link to a Honeywell site that explains it in simpler terms.. The part about shorting the two wires together and then opening them will aid you in identifying where the problem actually is.. here is the link: http://homerepair.about.com/od/heatingcoolingrepair/ss/thermostat.htm

Hope this helps you more than confuses you..
Regards

What you can do is try and clean the contacts. Open the door on the thermistat and remove the two screws, after that you can seperate the part that is mounted to the wall and the front panel. Look at the part that is mounted on the wall and you'll see the contacts that should be a copper color. They might be black from age. Clean them and you'll be surprised how well it will work after that.

Denis