thermostat incorrect vs actual temperature

[jalapeno]

my house is 4 years old. it came with a cheapo thermostat control (just a lever and a gauge type thingy), which i replaced with a programmable thermostat (last year). It seemed to work ok last fall/winter, but this fall i noticed that it shows incorrect temperature - e.g. displays +20C but it feels like +15C, especially on ground floor. When I crank it up to 22, the heat does come on and the house warms up to what indeed feels like 20+.

Where does this stupid thing get its temperature reading? Does it have a sensor inside or does it get it from furnace itself?
Thermostat manual doesnt mention anything about temperature calibration or this problem.

Any ideas?

[HayZee518]

the cheapy thermostats as you say read directly off a coiled spring and pointer inside. the programmable units use a thermister inside. this is connected to a b/d counter which powers the liquid crystal segments. perhaps your calibration is off a touch.