The inducer should only run when there is a call for heat. Since the furnace shuts off correctly when the set temp is reached, I will assume the call for heat is also off. But to be sure, find the with from that connects to the W terminal (heat) and disconnect it (TURN OFF POWER while doing this). Set the thermostat so there is no call for heat. Now if the inducer cycles when you turn on power to the furnace then I would say your control board is flaky. If the inducer does not behave abnormally (no cycling), then investigate the thermostat. With the W wire still disconnected at the furnace, check the voltage (carefully) at the W terminal at the thermostat (between W and Common). Since you are not calling for heat, there should be 0 volts AC. If you see intermittent voltages, your thermostat may be flaky.