Furnace Failing To Ignite...

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Old 10-16-08, 08:10 AM
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Furnace Failing To Ignite...

My gas furnace with electric pilot lighting is having some problems. When I first turn it on it starts up and lights fine and heats great...however when it turns off and tries to light again next time it's called it doesn't ignite. There error code given is Soft Lockout - Failed To Ignite After 4 Attempts.

What are some things that could be causing this?

As I said, everything works fine initially, it's just that when it tries to light again it fails and waits an hour before it will try again.

Thanks,
Paul
 
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Old 10-16-08, 04:27 PM
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Heat is maybe expanding something after the first time. It could be gas or electrical/ground connection related.


What is it that lights your pilot. Repetitive sparking? A glow coil?

And regardless which it is, does that function work first, and yet no pilot? Or does't that function work? Or does the pilot light even for a moment, but then go out? If it lights, does it stay lit for about 4 seconds, but then go out? You can go in the big panel of the furnace and watch, and then come back here and say.
 
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Old 10-16-08, 04:43 PM
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Originally Posted by ecman51` View Post
Heat is maybe expanding something after the first time. It could be gas or electrical/ground connection related.


What is it that lights your pilot. Repetitive sparking? A glow coil?

And regardless which it is, does that function work first, and yet no pilot? Or does't that function work? Or does the pilot light even for a moment, but then go out? If it lights, does it stay lit for about 4 seconds, but then go out? You can go in the big panel of the furnace and watch, and then come back here and say.
There is a heating element that glows orange when hot and after a few seconds there's a click sound and when it ignites the flames light up and we're good to go. When it doesn't light, it does sound like it's on for a few seconds (can't remember if there are flames, but it definitely sounds like it, I'll have to check it and get back to you) then it clicks off and then the heating element cools down and then tries again after a few seconds...then it just stops after 4 attempts of that.

What would it mean if it stays lit for a few seconds then goes out? I think that's what it's doing.

Thanks!
Paul
 
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Old 10-16-08, 06:10 PM
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I have a miller furnace that did the same thing. We had problems with it for 4 years, and prior dad did also. About 3 years ago a professional came out and replaced the gas valve, 380.00 OUCH! Still didn't fix the problem. He said it was the gas valve and he kept the combustion chamber plate off the heat exchanger and said we had a weak blower. Well anyhow with it kicking on sometimes, I had realized that the first 2 burners would ignite but not the rest. I removed the second blower, and the little gaps in the burners were plugged where they carry gas to the others. I cleaned all them out, and not a single problem. Our furnace is 15 years old, and I am more than sure when we were charged, there was nothing wrong with the furnace. It was a plugged burner. Might be worth checking.
 
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Old 10-16-08, 06:46 PM
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As Layne said, dirty burner crosslighters may cause this problem. Also, I would suspect the flame sensor. It is the rod with one wire connected on the opposite end from the ignitor. Remove and clean the burners, and the flame sensor and reassemble . Make sure burners are aligned correctly and use a scotchbright pad to clean the sensor.
 
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Old 10-16-08, 10:48 PM
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This is a video of exactly what's going on:

1st part is it working correctly, second part is it failing to stay on right afterwards.

http://www.paulferree.com/furnaceigniteprob.wmv

Thanks
Paul
 
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Old 10-17-08, 07:12 AM
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Looks like it could be a dirty flame sensor. It would most likely be on by the last burner on the right. It is just a rod that has one wire going to it. Clean this with some scotchbright or a dollar bill and reinstall. Do not clean with anything to abrasive.

See if this helps.
 
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Old 10-17-08, 08:28 AM
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Great video. As HVAC122 suggests, it sure acts like the flame sensor needs cleaning.

Remove it before cleaning, usually one or two screws hold it in place. Make sure the wire is connected to it when you reinstall it. No need to remove the wire, but it might come loose.

Just a note for the future, When the furnace goes into lock out, turn the power switch or breaker for the furnace off, and then back on. That will reset the furnace.
 
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Old 10-17-08, 11:09 AM
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I couldn't tell for certain if there were three burners or four. If four, and the fourth burner is not igniting then that is your problem as the flame sensor is located in the fourth burner.

Look for the "runner" passage between the third and fourth burner and make sure it is clean. If it is then look for a fouled or damaged orifice in the fourth burner.
 
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Old 10-17-08, 11:13 AM
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There are 3 burners, the middle one had the sensor. I couldn't disconnect it because the screw was in an awkward place. But I could reach it from beneath. I used a dollar bill and rubbed it on it and at first blush it seems to have worked. It's not cold enough right now to let the heat run, so I'll wait until tonight to see if it worked. But, so far so good! Thanks!!!!!

Paul
 
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