Hey guys, I've been looking through these forums but haven't found an exact answer to my question, so figured I'd start my own thread. I have an American Standard gas furnace that uses a glow plug-style ignition system to light the gas, but the furnace only blows cold air. Let's see if I can get all the details here... The problem started a couple days ago with the furnace blowing cold air after being turned on after turning off the thermostat for the night. I went down to the basement and read the panel, turning the gas switch off, then the power, then back on. Once back on the glow plug lit up, a few seconds later I heard the click of the gas turn on, then the burners lit up and everything worked fine. The same problem happened 2 nights ago and was resolved in the same way. This morning, same thing, only now the furnace won't light up. I watched a cycle - hopefully this helps in diagnosing what's going on... after shutting everything down, and turning the gas and power back on the glow plug lights up. The gas clicks on and a few seconds later the gas tries to light (I see a flame start in 2-3 out of the 6 burners) but then everything quickly goes out, including the glow plug. There seems to maybe be a timing issue where the glow plug lights up brightly, then almost turns off? A split second before the gas comes through the burners. It doesn't go out entirely when the gas kicks on, but its dimming at the exact time the gas flow starts. I don't remember if this happened before when I got the furnace to work, but I seem to recall the glow plug glowing brightly throughout the ignition process. As background, I've lived in this house 4 years and have never changed the igniter (glow plug thing) and I read in a different thread the life span of these is usually 2-4 years. I wasn't thinking this was the problem since it does light up and glow brightly, but I'm no expert :)

Thanks for any help you guys can give!

Andrew

Usually if the glow bar, plug, or ignitor works it is OK. You might need to clean your Ignition sensor which is located in the same general area as the glow bar/plug/ignitor. < all the same but usually called ignitor. Note do not touch the ignitor with your fingers. The acid on your finger tips can cause them to fail prematurely.

Thanks! I'll try that tonight before I call a service tech. I did get the heat working intermittently last night / this morning. It seems if I keep reseting the furnace eventually it catches and the burners ignite. What does the ignition sensor look like? I read you can clean them with sandpaper, is that right? Thanks again for your help!

Sand paper will work fine.