OT - goofy thermostat no manual

I'm working on an old 116 year old farm house for my daughter that has been vacant since September and it has a 4 year old Honeywell TH5110D1006 thermostat that won't accept a temperature set point. I can arrow up the temperature set point to get the "heat-on" prompt but as soon as I release the up-arrow button the temperature I want immediately winds back down to 40°. The bottom buttons are also locked into the fan-auto & heat-mode and won't change. It does have 2 brand new / tested batteries. Appreciate any help.
 
Must be somewhere on the back? I already did peel off the paper label on the thermostat's back behind the arrow keys - I'll have to look closer. Thanks!
 
Thanks, leaning towards installation set-up code is wrong. May have fiddled around enough to change code from LP w/AC furnace to one with heat pump.

One of those "rule of 3" things going wrong last night. No heat, battery went dead on my Toro workman and had to walk home to a worried wife that had supper waiting and then discovered that the drive is apparently crashing on my 14 year old HP computer. Did finally downloaded PDF of thermostat.
 
Did determine code was correct, however, absolutely wouldn't hold temp setting or respond to any inputs. Took it apart and sprayed circuit board with contact cleaner and put back together. Works great now! Moisture or some sort of film from sitting too long maybe? Thanks to all for suggestions.
 

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