When thermostat turned to heat, furnace lights and burns good. When blower comes on flame slightly flickers but still burns pretty good. Flame goes out before correct temp is reached. Blower continues to run and lighter glows again. Blower stops before gas valve opens and reignites. Flame burns even and good. When blower comes back on the second time, the flame in the left side of the heat exchanger is really blown about. The flame continues to burn but the flame shoots out past the access cover and has to be manually turned off at the thermostat. A few times, the furnace lights and burns evenly until the correct temperature is reached, the gas valve closes and flame goes out. That only happened twice in the dozen times I tried it. The other times flame shot out past the access cover. I was told it had to be a hole in the heat exchanger but why does it sometimes burn good? Thanks for your response. Doug

Sounds like a possible bad heat exchanger,, I would get it checked out ,it could be dangerous