Yup like stated above, it's probably an on/off thermostat, meaning it stays on until temp is reached, and as it cools, it kicks in again to bring temps back to whatever u set it at. If your looking for a digital proportional, look into a Herpstat. It gives constant power to reach desired temp, then pulses to stay at that temp. They work very well, I have 2 and wouldn't trade them for any other thermostat!