It seems that my furnace is not kicking on when I think it should, it is colder in here than I have it set. I seem to be able to "jump start" it by turning the emergency switch off and then on. At that point, the furnace will turn on and do its thing - blow air for about 3-5 min or so, then turn off. I wait for it to kick back on to continue heating, but most of the time it doesnt and I need to repeat the above. What could be causing this?