Do You have a HVAC Unit or a Heat Pump ?
Make sure that the Thermostat Unit is LEVEL. (If it is an older model with the Mercury Bulb) if it’s a newer version then it’s probably a Factory Defect and needs to be replaced.
Dude
“Make sure that the Thermostat Unit is LEVEL. (If it is an older model with the Mercury Bulb)?”
That comment makes you look old. I got one of those. 😁
I’d go to Lowes, HD or Amazon and buy a new one and install it. That’s not hard to do, just a couple of wires. Take a picture of how the old one is wired with your phone and rewire the same way. Also check before removing the old one that the wires are attached matching color to matching color, i.e., black to black. If that doesn’t fix it, then it’s probably not the thermostat. It may be at the other end in the furnace itself, or if you have a heat pump have them check the setting on it. They are usually set to read outside temp and switch from heat pump to standard heat at a set temperature. Ours is set at 40 degrees. If you have a heat pump, try setting the thermostat on emergency heat. That takes the heat pump out of the equation and runs the unit like a straight up gas or electric furnace.
Hope some of this helps.