Ok I just finished installing a downflow furnace in my garage. The unit was new never installed before. The model is GNL100N16G1 manufactured by International Comfort Products Corperation. I finished the install and turned her on. She fired right up and ran perfect warming the garage to 65 degrees in less than 15 minutes. I left it on running while I cleaned up the garage. It cycled on about 4-5 times while I was cleaning up. Then it turned on and had no heat. The small exhaust fan was running and the big blower was runnning but no flame ( = no heat) . I turned the system off for 10 min. and turned everything back on and the exhaust fan turns on but the ingnition system will not light the pilot. It will just cycle through this process and never light the pilot?? I have read the manual and checked some sites and can not figure this out. Can anybody help me with this problem?? I am at a loss right now. It worked perfect for about 2 hours cycling through the system as it should and then this. Please help!!

You need to make the furnace go through its' cycle while you are there watching what it does. After the vent assist blower comes on there should be a hot surface ignitor that starts to glow, as it gets bright hot the gas valve will open and the hot surface should light the gas. If it does try to ignite the gas but goes out immediately then it could be the flame sensor is dirty. This sounds impossible for it being a new furnace but with all of the work around it it could be dirty. You can take the sensor out and clean it with some fine sand paper and re-install it and see if it works.

If the hot surface ignitor does not ever glow, you need to look at the ignitor to see if you see a crack or some white on it. If you don't see a crack disconnect the wire and use a volt meter, insert the leads into the wires that the ignitor came out of. Now again start the furnace and watch the meter and see if the meter goes to 120 volts at the time that the ignitor should be starting to glow. If you do have voltage that means that the ignitor is bad. If you do have to replace the ignitor do not touch the carbon part of the ignitor with your fingers because the oil on your skin can cause the ignitor to fail.

If this helps you please rate my answer.

Thanks. Yes the you are correct that the igniter does not glow. I checked what you said and there is no cracks the glow plug looks brand new. There are three wires 2 blue that go to the igniter and a black.(I assume a ground) I checked the volts where the to blue wires connect and I get a reading of 24.6v. When I put the black plug to the ground and the red plug to one of the blue wires I get 103.2v. What does this mean?

Also the transformer makes a hum sound. Is that normal. I don't here the hum on my home furnace. Could this be a problem. It is weird that the furnace worked perfectly the first couple hours. Why all of the sudden would the surface igniter stop working? Is there a reset or something I need to trigger?

Update. I checked the igniter and get no resistance in the igniter. SO I assume the igniter is bad. Am I correct? And why would this igniter only work for the first couple of hours and then fail? Can something else cause this igniter to fail? I am just trying to understand why a new unit would fail so quickly. And also would like to know if the hum in the transformer is normal. Thanks for the help.

I am not familiar with your furnace but I can tell yo that a transformer almost always will make a little noise, if it is really loud you might try moving the transformer with you hand, just a little pressure and see if it changes the hum.

About the ignitor. Things are put on furnaces to go bad!! Honestly I am not sure what has happened to yours and the voltages you reported do not jive with most ignitors I have worked with.

If no resistance at igniter, then I would start by replacing the igniter.

Slight humming of trans if normal. Sometimes you just get a unit with a bad part form factory, or it may have been roughly handled during delivery. If you installed this unit yourself, and you are not a licensed furnace installer, your warranty has most likely been voided. So just replace the igniter and let us know if it works. If it doesn't, come on back and we will try our best to help you locate the problem. (could be a pressure switch problem, as I've never seen these voltages on an igniter)

Yea I hate these igniter's. I like the old fashion pilot light. This furnace was bought from a friend that had it sitting around for over 5 years and when he bought it it was 2 years old. He just never got around to installing it in his pole barn. So the warranty is way gone. I only gave the guy a $100 bucks for it. This part is going to cost that much I bet. Is there any online retailers that sell parts cheap. I would like to spend as little as possible as this is just for a garage. The Tempstar replacement part was like $329.00 dollars from them. I know I can find it cheaper than that.

Go to the following web page and see what you can find
furnace hot surface ignitors - Google Product Search

Yea did that and found it at partsguy.com for $49.90. Much better.

Well I received the new part and installed it. Furnace works great now. I checked the old igniter to see why it failed and guess what I found? Behind a sticker on one of the wires was a cut that could not be seen because of the sticker. The furnace must have had just enough resistance to make the glow plug work for a little while. And with a little vibration the wire must have separated a little more resulting I the no resistance in the part. So I now have a spare igniter as I was able to rewire the igniter. And I now get the same resistance as the new one. Live and learn. Before I order any other parts that have wires on them I will give them a good inspection to be sure there are no problems.

Never hurts to have a spare igniter around. Glad it fixed your problem. Take care.

Lee