I have a 1980's gas furnace I believe the manufacture was Day & Night. My problem that just started tonight is that it turned itself off. It brought itself up to its desired temperature and then hasn't come on since, so it has gotten cold and the heater won't turn back on. I went through the trouble shooting steps on the front turning the temperature gauge down, turning off the power and turning off the gas for approximately 5 minutes. afterwards I turn all the things back on and then turn the temperature back up. it will start running until it gets to the desired temperature and then it will shut off again. can anyone help. does this furnace have a safety that it is activating?