This furnace will come on normaly...ignitor glows, gas comes on , burners fire up, blower comes on, burns about 3 minutes,gas shuts off, blower still blowing to cool down...then ignitor glows again,gas comes on, they fire up,blows out kinda warm air,then runs about 3 minutes, shuts down,blower still blows and goes through the whole thing again. never shuts off.We have replaced the limit switch. the board flashes the red light but I can't find the "default codes" sticker that tells what the flashing light means.Thanks for any help. Tamara