FURNACE CYCLING ON AND OFF ..

It sounds like you have a dirty or faulty flame sensor im assuming that you have inshot burners in your furnace the flame sensor will be on the right or the left of the burner assembly opposite the pilot and ignitor it slip through the burner assembly and attaches to the burner it is l shaped steel that is fitted in a porcelin housing and when installed correctly it will be directly in front of one of the inshot burners when the main burner lites the flame touches the sensor and holds the gas valve open until the thermostat is satisfied remove it and sand the the l shaped metal end with 100 grit sandpaper until its clean and shinney then reinstall set thermostat to heat and see if it will stay lit if not get furnace brand model and serial# go to local hvac parts house and pick a new flame sensor if its a rheem i generally pay about ten dollars each my cost chances are cleaning will take care of the problem. good luck! hvac ike

I would check furnace filter first. If that looks good i would check the thermostat. To check thermostat turn power off to furnace then take thermostat off the wall and connect wires labbled R & W together then turn power on and check furnace to see if it runs for more than a couple of minutes. If so install a new thermostat. If that doesn't work let me know and i can give you a couple more thing to try.