In April 2013, furnace would not blow hot air, motor was running but no air blowing. Service tech replaced thermostat. I guess it was fixed but probably did not use too much since it was Spring then Summer. In October, no hot air at times but motor running & motor getting way too hot. Service tech came & said heat exchanger failed, 320+ ppm CO in outside exhaust but none in house. We were shown how to hit furnace inside of panel & then something would engage and the gas pilots would start on fire (I look into this little window & see fire) and it would work! Now, no amount of hitting gets fire to come on. Motor runs, no heat. It is an older HEIL. TY.