Hello,
I have a Sears Fifteen Horizontal furnace that will come on and then go out before the proper temperature is achieved. The fan will continue to run but the burner will not re-light until I reset it at the thermostat.

Also, I had the blower motor replaced several years ago and the tech set it to run an extended period after either the heater or AC finished it's cycle. I would like to set this back to the normal run time. Any suggestions with either of these questions would be greatly appreciated. This is an electronic start unit and I believe it is 15-20 years old. Thanks again.

First it wpo;d help to know who made that furnace for sears? There is a lot of ways furnace manufacturers adjust the time off fan, dip switch's, small jumpers etc. As for the burners cutting out that is usually a weak main limit or overheating caused by low airflow.

I knew that question was coming. I have looked all over this unit and I am unable to locate the manufacturer. However, I will look once again.

I did remove the cover to the igniter and heat sensor, brushed them off with a paintbrush as well as tighten a loose ground connection and now the unit is coming up to temp properly.

Again, I appreciate your assistance and will get back with the model/manufacturer when I locate it.

Clean they flame sensor with steel wool,fine grut sand paper or crumpled aluminum foil, I don't think the paint brush is sufficient. Good Luck

I have a similar problem with a Sears Fifteen Natural gas electronic ignition furnace. When the thermostat calls for the furnace to come on, the burners come on at a low level and then almost immediately, I hear a "rattling" sound and the furnace shuts down. If nothing is done, the furnace never comes on again. However, if I shut the thermostat off and wait a couple of minutes, the furnace will light up again. Sometimes, this has to be done thrice to get the furnace to run. Then it usually functions OK for the rest of the day. I had this problem 10 years ago and cured it by sand blasting the igniter/sensor (looks sort of like a apark plug with three "prongs"). It worked flawlewssly until reccently and then statrted the problem again. This time I bead blasted it and it it notably better, but not 100%.