Did you change the batteries because it displayed the word Battery on the screen?And did the terminals where the batteries make contact look corroded at all?JACUSTOMER-t1xxi9wu- :The terminals do not look corroded.I changed the batteries because the old ones died. when i put in the new ones, it worked fine, then didn't.I am using lithium AA batteries now, not alkalineMatthew :The thermostat will not recognize new programming if the programming is done with the batteries in a low state. I am thinking that the terminals are losing their conductivity and not recognizing the full power of the batteries so it is not allowing you to store new programming optionsJACUSTOMER-t1xxi9wu- :It stores the new program just fine--if i leave the cover off and don't touch it, it's fine. but if i put the covr on fully or if i over-ride the program (for example, raise or lower the temperature manually), then the whole thing reverts.Matthew :The manual says that it will hold it for 10 secs then go back to the settings before the changes when the batteries are low. Try setting it then don't put it back on for at least 10 secs and see if it goes back.JACUSTOMER-t1xxi9wu- :i have done that several timesMatthew :There is no reset or anything like that that would cause it to go back to the default settings.JACUSTOMER-t1xxi9wu- :so i am thinking that the cover trips something when i replace it--it has never done that before but now does it all the time.Matthew :The only thing the cover could be doing is pressing against these batteries and causing them to lose connection.Try taking that little flap that the battery's rest against and bending it out so the batteries fit in there as tight as possibleJACUSTOMER-t1xxi9wu- :If that's true, how do i fix it? The batteries are jammed in tight!!I think I might need a service call in my home--do you know of White Rodgers Service people in Berkeley California?Matthew :White rodgers don't have service people they just sell to the general public and to dealers like myself. There is nothing ordinary going on with your stat there is no reset option or anything like that so I'm afraid your stat is just malfunctioning and you need a new one. This thermostat isn't even made anymore it has been re-engineered and replaced with newer models.http://www.emersonclimate.com/en-US/products/thermostats/Pages/programmable_single_stage_thermostats.aspx#1F80-0471This is a list of White Rodgers brand thermostats that are currently being sold. Any brand of thermostat will work for your system i would look into Honeywell they are my thermostat of choice but it is just because of the ease of installation for me personally.JACUSTOMER-t1xxi9wu- :My problem was not solved.Matthew :Your solution is a new thermostat I'm sorry but that is the answer.It is a thermostat last used back in the mid 90'S and it has gone bad they do not last forever.