Gas Furnace Failing to Ignite

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Old 01-06-10, 08:34 PM
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Gas Furnace Failing to Ignite

I have a Goodman furnace that's been running well for several years until today. Now, when the heater cycles on the following occur:

The vent blower comes on normally, the ignitor makes a spark, the gas comes on but does not ignite. It retries a couple of times and eventually the system shuts down. The LED flashes 1 blink.

According to the note on the inside of the heater cover, one blink indicates ignition failure and lists the following as possibilities: gas flow, gas pressure, gas valve and flame sensor.

I think I can safely rule out gas flow and gas pressure, as I am able to hear and detect gas coming out of the three jets and the rest of the gas appliances in the house operate normally.

Which leaves the gas valve and the flame sensor, or something else.

My questions:

How likely might it be that the gas valve is malfunctioning if there is flow and pressure? Should I even consider it?

Even though the gas is not igniting, how likely is it that the Flame Sensor is the problem?

What else may I be overlooking?

It is a Goodman (or GMC) GMP075-3

Best,
Yak
 
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Old 01-06-10, 11:08 PM
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The manual for your furnace is here:

http://site.famousparts.com/goodman/PDF/IO-137.pdf


Your furnace has a hot surface ignitor that should glow white hot to light the gas. However, you describe a spark.

IS the ignitor turning on and getting white hot? Please describe the spark in more detail.

Page 17 of the manual describes the sequence of operation when the furnace is in heating mode.
 
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Old 01-07-10, 04:52 AM
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Thanks for your reply.

The sequence on page 17 seems right with the exception of your description of the igniter glowing white hot.

The ignitor does not glow white hot. There is a spark.

The gas does come on, and I can hear a snap as a spark occurs however, the gas does not ignite. The system cycles three times and then shuts down. The smell of gas is apparent.
 
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Old 01-07-10, 05:37 AM
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In an intermittent pilot ignition system, the usual reason that the pilot wont light off the spark is that the pilot burner is dirty and the pilot burner and pilot orifice need to be cleaned.

You will need to use a 7/16" wrench to loosen the brass ferrule holding the pilot tubing into the pilot burner. When that's removed you get access to the pilot orifice which needs to be cleaned. Some pilot orifices can be cleaned using the wire from wire brush, others have holes that are too small for that and you may be able to clean it with some compressed air. If you can't get it clean that way, you may need to shop for a replacement.
 
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Old 01-07-10, 06:05 AM
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Hmm. I think, at least according to the manual that you sent, that is isn't a pilot-based ignition system, but contains an ignitor. It's definitely electrical and is shaped like a long, skinny "U" (on the diagram on page 25 they call it an HSI).

Questions:

Is that what should be replaced, or are there other components behind it that commonly fail that I should consider?

I'm also having a little trouble finding heater parts retailers. It's not like it was when I was a kid when we'd go to the hardware store to get what we needed. Most places are "service only." Do you have retailer suggestions?
 
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Old 01-07-10, 09:07 AM
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All right ---- a hot surface ignitor system is certainly what I'd expect from that furnace, but you never know what a manufacturer might have installed in some units, and I would argue with someone who saw that they had a spark ignition system.

But now I am confused. I take it you are now saying you do have the hot surface ignition system. Is the ignitor glowing white hot to light the gas? If not it may need replacement.

Are you seeing sparks in the furnace? If so, where are they coming from?
 
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Old 01-07-10, 12:59 PM
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I took your suggestion and drove to the other side of creation to find a new HSI. Once replaced, the system came back online.

It cost about $30 and I found it by looking in the online Yellowpages for "Heater Supply" and then calling about 8 businesses before finding one that sells to the public.

The old HSI was actually sparking --as in, it would "pop" momentarily with a flash, and did not glow. I can't see behind the burner where it is attached, but maybe the old one was somehow arcing to ground(?)

Anyway, I'm grateful for your assistance in helping me to think it through and for posting the link to the manual so that I could start to familiarize myself with the system before taking any action on it.

All the best,
Yak
 
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