I have a Ducane Furnace that is roughly 6 years old. It includes Central Air. The past few weeks we have noticed that there are times where the temperature in the house is way (like 2-3 degress) lower then the temperature the furnace is set at (which is usually 68-69 degress) In order for us to get it to kick back on, we have turn the thermostat off, and then wait like 30 seconds and turn it back on again, hoping the furnace kicks on. I have had my furnace cleaned and inspected and its running awesomely as the tech told me. I have also had the thermostat replaced with the a new one- same model and brand. Any ideas what could be causing this? Its getting quite annoying.