Goodman Intermittent Ignition Failure


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Old 02-25-08, 05:41 AM
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Goodman Intermittent Ignition Failure

We have a two story colonial with 2 Goodman LP gas furnaces, one furnace for each floor. The furnace in the attic is a Goodman GMS8 single stage unit and is about a year and a half old, as is the house. It's controlled by a Robertshaw 9600 programmable thermostat. We live in northeast Masachusetts where overnight temperatures fall into the single digits or teens on a fairly regular basis.

The attic furnace will periodically fail to ignite. It's apparent in the morning when the thermostat calls for heat at 5:30 AM, but I believe the problem happens at other times of the day as well (however we're not upstairs much during the daytime). After three attempts it goes into its safety lockout mode. Then after an hour it tries again and usually starts. Based on the manufacturer's diagnostic chart I would expect to see the diagnostic LED flashing once, but when I look through the plastic viewport the LED is not illuminated at all. If I manually reset the furnace by interrupting the 115 V supply and the furnace starts, then the LED is illuminated constantly as it should.

The gas pressure has been checked on both sides of the gas valve, the hot surface ignitor glows as it should, and the flame sensor looks OK but I haven't cleaned it or tested it.
What would cause the diagnostic LED to not be illuminated after a failed ignition attempt? Do I have an intermittent problem with power to the control board? If there was no low voltage power to the board it seems as though the furnace couldn't even attempt to ignite. Is my control board bad? I have a digital multimeter but since this is an intermittent problem I'm not sure what to measure. Actually, as I think about it, I maybe should check the power to the control board next time the furnace fails to ignite. If I have 24 V (or whatever the low voltage supply is) then does that condemn the control board?

My previous houses had oil-fired hot water boilers. With those, you got one 45 second attempt at ignition and then the system went into lockout. You had to manually reset it to get another ignition attempt. With gas furnaces, it seems the ignition reliability is much lower. On each cycle you get three tries and then after an hour you automatically get three more, then another three, etc. Why is it gas furnaces have such greater difficulty with ignition?
 
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Old 02-25-08, 07:28 AM
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I think your model has an induced draft blower, but any problem with that or the pressuer switch should set a code.

One thing that these furnaces with electronic controls are sensitive too is a good ground on the incoming power. You could check the outlet and the plug. They will act up if the ground is poor.

I think Goodman has a tech number you can call.
 
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Old 02-25-08, 09:01 AM
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If the sequence you observe is: inducer fan goes on, ignitor glows, main burners come on for a few seconds and then go out, and then the furnace shuts down - odds are the flame sensor needs cleaning. Remove the flame sensor and wipe it several times lengthwise with fine steel wool. You just want to clean it, not polish or remove metal. Reinstall and check furnace. Should be running.
It's an annual maintenance job on my Janitrol (Goodman) furnace.
 
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Old 02-25-08, 10:27 AM
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I have only observed the start up cycle with the access cover removed once when the furnace tech was at the house. The sequence of events was: inducer fan spools up, ignitor glows brightly, gas valve opens (as verified by digital manometer), gas does not ignite, furnace shuts down. After a few seconds, it tries the same thing again. The tech adjusted the gas pressure upwards somewhat to about 12" on the input side and 10" on the manifold side.

Now that I understand the expected sequence of events, I listen very carefully in the morning when the programmable thermostat calls for heat. The furnace is directly over the master bedroom and it is very quiet where we live so I can hear quite well. Here's what seems to be happening: inducer fan turns on (that's easy to hear), ignitor lights up (I can hear a relay click), no flame gets established (when the flame does light you hear a roaring sound), furnace shuts down. Since the gas valve was tested by the tech I'm assuming it's working OK. After a few seconds it goes through the same sequence including the shut down. After another few seconds the same thing happens and now the furnace gets a time out for an hour. After an hour has passed and it tries again it usually lights up.

I should emphasize the furnace starts up without problems much more often than it fails to light. Typically, it fires up on the second of the three allowed tries per cycle.

The thing that puzzles me is why I don't get the flash once LED signal to signify a failed ignition attempt. Of course, I also don't understand the periodic failure to ignite properly.
 
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Old 02-25-08, 11:10 AM
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If what feeds your furnace is propane, then the gas pressure settings seem o.k.

Do you have propane or Nat. gas there?
If you have nat. gas, then the pressure settings are outrageously high and may explain why the failed ignition attempts (the mix is way too rich in gas)
 

Last edited by pflor; 02-25-08 at 11:59 AM.
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Old 02-25-08, 05:35 PM
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The furnace is fueled by liquified propane gas. There are several decals and stickers that indicate the furnace has been converted for use with propane.
 
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Old 02-26-08, 02:07 AM
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Originally Posted by BikerBill View Post
My previous houses had oil-fired hot water boilers. With those, you got one 45 second attempt at ignition and then the system went into lockout. You had to manually reset it to get another ignition attempt. With gas furnaces, it seems the ignition reliability is much lower. On each cycle you get three tries and then after an hour you automatically get three more, then another three, etc. Why is it gas furnaces have such greater difficulty with ignition?
Actually, you kind'a get more for your buck with gas
I mean, with oil, you get one shot at ignition and the primary control goes right away into lockout mode. With your unit now your have "3" trials for ignition prior to the module going into lockout mode. With oil you push the red reset button of the primary control...with gas you flip the switch OFF and ON.

And the only reason why your furnace goes to only 3 trials for ignition and does not just keeps on going is "safety". Propane is heavier than Natural Gas, so you don't want an accumulation of unburned fuel around the furnace. Same deal with oil, but you get only one shot at ignition there.

The problem you are describing is quite unusual. I'm going to be doing some reading here (in particular regarding the module's apparent misbehavior with its status code light), but at this time at least, I can tell you this much: regarding the gas valve getting its juice and not lighting up, it occurs to me that it can be one of two things: (1) A defective gas valve (with an intermittent problem) that fails to open even though its coil is getting 24V, or (2) a clogged (or partially clogged) orifice in front of the igniter
 
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Old 02-26-08, 02:43 AM
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Troubleshooting charts

As applicable to your furnace, for the reported problem.



Just perform the tests mentioned on paragraph-1 above before condemning the board. Hope this helps. Feel free to get back in the forum with additional questions if you'd like other feedback.
 
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Old 02-26-08, 10:06 AM
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pflor,

For some reason, when I went back to re-read your response all of your inserted text was gone. I'm wondering if you can just e-mail it me. I actually have the matrix format troubleshooting chart from Goodman but you had some comments before the matrix chart I wanted to follow up on. Thanks.
 
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Old 02-26-08, 11:04 AM
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Sometimes all it takes is a click on the "refresh" button and the pictures/text will show up. The photo-upload site may have been down. Try again. It's there, I can see it.

Yes, I could e-mail you the info., but posting it on the forum may prove helpul to others as well. And besides, I don't know your e-mail address
 
 

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