I replaced my old thermostat (Lennox) with RTH7500 and it still won't work a/f I looked over the wiring twice. I even had the technician on the phone help me.

Oddly, I can't even find the Y2018 model on the Lennox site nor on the entire internet. I looked at a 7500 comfortsense manual and no where in that manual is a battery mentioned. Some thermostats do indeed contain batteries to preserve settings.

The Lennox home site seems to direct people to Lennox dealers. If the manual for your thermostat does not include a support number other than warranty, you may have to talk to a dealer/installer. Sorry.

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

well the wire on x will go to e thr r is the red wire goes to r the wire on f willgo to g the y will go to y now the rest you'll have to verfy at air handler o will go to reversing valve common wire will go to c the electric heat will go to aux

Hope this helps Lennox iComfort Thermostat Wifi Server Connection Issues

What is the model number? I have an SLP98 (installed on 11/29/2011).... and if I take the cover off the front of the furnace the panel that has the fancy "Lennox" badge on it) you will see two clear round windows about the size of a half dollar (one high on the furnace box and one lower on the blower box.) If you look downward into the window on the blower box you can see a red LED display that will sometimes flash error codes like E228 (one character at a time). If your model has something like this, let me know. I've done some DIY fixes recently out of necessity....and their easy.....and several technicians confessed they didn't know much, if anything, about the newer high effieciency Lennox gas furnaces.

What is the model number of the old tstat and furnace?

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

red to rh green wire to g yellow wire to y1 white wire to w1

You have a control board on your furnace, there is a 3 amp fuse there, that 3 amp fuse needs to be replaced. You most likely touched a wire even by accident and blew the fuse. You will have to remove the door \panels to get at it. It looks like a normal car fuse

Make sure on the furnace that you have the same colored wires connected at the thermostat to R and W. Check for good connections at both locations. You can always test to make sure the unit fires by crossing the two wires together. If the unit fires, you have a bad thermostat.

Hello,

I had exact same problem with RTH7500. Did not set the date properly at the beginning and than realized that there is no menu option to change the date after it is saved once (???!). I was very confused for few hours and wandering - trying to find changing option on thermostat menu; than I was looking online what can be done... I could not find solution...

Than I took out both AA batteries, open the thermostat (be very careful while doing this - you don't want to break plastic peaces that hold the thing together) and took out the button battery thinking that this will reset the thermostat... but it did not.

I repeated the same thing, but this time, while the button battery was out, I put two AA batteries back and this reset the thermostat... the old - blinking date appeared and I was very happy to see this on thermostat screen! This time I set the time properly and it works fine.

:)

Hope this will be helpful if you did not solve the issue yet... if you did, someone else might find this solution useful.