Winter Furnace Outage of 2011

So two nights ago, my family and I returned home and the house was super cold. My wife asked me if I turned off the heater while we were gone, I immediately know that something was wrong. When I went over to take a look vents, it was just blowing cool air. At the furnace, the blower/fan was running, but there were no flames in the burner. So my trouble shooting begins.

My particular furnace is an Armstrong Ultra Sx80 Natural Gas fired furnace.

1) I checked online and the information that I found was that most likely what happened was that the filter was super dirty and because of this the lack of airflow caused one of the safety switches to trip and prevent the auto pilot lighter to ignite. So what I found out is that there are couple of limit switches and resetable roll-out switches right above the burner. Of course, I changed out the filter above the blower and look for the resetable switches. Once I reset the switches and check the resetable switches with a voltmeter, everything looked good, and …. no fire :(.

2) I then looked online where people said that there could be blockage on the pressure switch and in the hose, so I disconnected the rubber hose, cleaned out both side and check the pressure switch with my voltmeter, and … no fire. 🙁

I gave up and finally called a furnace guy. The guy showed up and was very friendly, check the basic things that I checked and said oh… your high limit snapdisc temperature breaker was tripped. It was the black connector in the back of the controller. He unscrewed it, pull it out and “smack” the breaker on the side, tested again with the multimeter and plug it back in. turn everything back on and poof!!! it fired up.

So with $99, I learned what a high limit switch/breaker looks like.
And the house is warm again!!!

The funny thing about this was that the furnace tech said that I am his second Electrical Engineer of the day. He said that his first visit today was also an electrical engineer.