My heating unit doesn't generate enough heat. Everything comes on but stops running before reaching room temperature. I've turned on and off the wall-thermostat and it works. Is this a sign that the wall-thermostat is going bad or went bad on me?

1st thing,jumper the red and white,thermostat wires,either at the furnace or the thermostat end,, if furnace works fine and doesn`t short cycle(cut off before it should),you probably need a thermostat