We bought iur house about a year ago (built in 1990) and just recently the downstairs thermostat won't let me turn it up in either heat or cool mode. The little "filter" icon was flashing so I just replaced the filter but the icon is still flashing. Not sure if that is related to the main problem or not.

So for instance I just turned it down from 74 to 73 but it won't let me turn it back up to 74.

Any ideas?

Can you post a photo of the thermostat, or at least try to find a model number on it? Based on your description it sounds like it is digital, but not one of the new "smart" thermostats.

It is unlikely that your system has a differential pressure detector, so the flashing filter light is most likely flashing based on the number of hours your fan has run since the timer was last reset. To make it stop flashing, you will need to reset it. If you can find a model number on the thermostat, you can probably find the manual for it online.

Not sure how to post pics here but it's a digital Austin Energy "Converge" model number 188-275. I'll have to Goigle it later.

Is it a White-Rodgers Comverge 1F88-275?

If so, it may have been recalled. You will have to check the date code; this will tell you where to look: http://www.cpsc.gov/en/Recalls/2011/White-Rodgers-Recalls-Home-Heating-and-Cooling-Thermostats-Due-to-Fire-Hazard/

Ok, I found the user manual, but I had to use the "Wayback Machine", so the link is a little wonky. http://web.archive.org/web/20101011204723/http://www.eon-us.com/dc/thermostat_manual.pdf
I don't have time right now to look further into it, but I'll revisit this later.

Thats awesome. I really appreciate the help!

I actually ended up just installing a new thermostat last night.