Hi, I have an oldersearsfrunace, not sure of the model.It has been recently upgraded with Central air andnew thermostates. The issue is the furnace ignites, and then after a few minutes it has an explosion, not big enough to do damage to the house YET,but it seems to be getting worse. Tonight I was sitting in my house, and the furnace "POPPED" 5 times in a row,hard enough to shake the windows and set off the burglar alarm. When I went into the furnace room to look, I could see that the furnace was lit, the pilot was working( electronic ignition) and the blower was on,then the blower went off aftert about a minute the blower shuts off but the flames stay on,then the blower will turn back on again. I turned the furnaceoff, waited a few minutes, removed the covers, cleaned out the baffles,replace the coversand still the furnace POPS. At first I thought the gas was not getting through into the burners, but they are all clear. I seen the gas ignite backout of the furnaceeven after the flames has been on for about a minute. I did notice that the temp inside the house does not get warm. I can keep the fan set to the on position, but it deos not allow the furnace to ignite when I do that..

Anyone please help,its gettgin mighty cold in hear.

Tim in Detroit

Call for professional service now. This is the best advice I can give you.

I second hvac1000's suggestion