Hello i find a 2509621 is this you model? if so a couple things to check. there is a reset in the top part of the furnace.look through the louvers ans you may see it.push in to reset and if it goes off again check the venting as this is a safety that tells if the vent is overheating. other thing to try. in the lower part where the pilot lite is you will see the gas valve. it has 3 wire connection points.one has a red wire with another wire. one has a white wire and one has another wire. use a paper clip or wire to jump the red to the other without the white wire this should turn the burner on. if this works check your thermostat/limit switch wiring. but by all means do not leave jumpered.