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Old 12-10-2007, 10:55 PM   #1
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Furnace Wont Stay On


Hello,

I have a Goodman Furnace (model # GMP100-3). The furnace will not stay running. Here is the sequence of events.
1. Thermostat Calls for Heat
2. Inducer starts
3. Pressure switch closes
4. Heating element glows
5. Burners Ignite (flames nice and blue, everything looks good)
6. Blower Comes on, House Starts warming up, but stops well before temperature is reached. There is no set amount of time for this (sometimes 10 seconds, sometimes 5 minutes)
7. Burners extinguish prematurely and blower continues to run.

Other info - The diagnostic LED flashes three times which means "pressure switch failure to close" and to check venter, pressure switch, vent blockage. I got a new pressure switch and changed it out (no improvement). I pulled off the flue pipe and checked for blockage and it is clear. I checked the hose running from the inducer to the pressure switch, and it is in good condition. I am leaning toward the high limit being tripped partly because the longer I let it sit, the longer the burners will run. If I let it sit for the full hour it takes to get out of lockout, it will come on and run for 5 minutes then shut down. If I then immediately turn it off and back on, it will only run for a few seconds or sometimes not at all, which is why I thinking the temperature is still too high, tripping the limit.

I guess here are the questions - Is it possible for blockage further up the chimney to cause this? Could I have a bad high limit and how do I check that? Could it be a bad inducer not keeping the new pressure switch closed? Do I have a cracked heat exchanger? I really don't know that much about furnaces, I have just been learning through forums like this and by fighting with this beast.

Thanks in advance for your help,
Mike

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Old 12-11-2007, 02:40 PM   #2
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Furnace Wont Stay On


MCCHEESE, I wish I could help but I have the same problem you have with my 1999 RUUD Silhouette ll. I will be watching out for the answers you receive and if you get good answer please send it to me at:carl300@gmail.com. I'll gladly let you know through this thread.
Thanks,
Carl300

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Old 12-11-2007, 05:04 PM   #3
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Furnace Wont Stay On


Try cleaning the flame sensor with scotch brite or a dollar bill. It is the rod attached to one wire on the oppisite side of the ignitor. Also make sure there is no buildup inside the hole on the inducer where the pressure hose hooks up.
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Old 12-11-2007, 06:46 PM   #4
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hvac122,

Thanks for your response. I have cleaned the flame sensor and used a small drill bit to check for blockage in the inducer. The drill bit goes in freely for more than an inch then feels like it hits something solid, is this normal? Should I try to force the drill bit in further, or am I only concerned with the opening? There isn't any blockage within the first inch, and I can feel the suction from the inducer when it is running. Also, I do not hear the pressure switch release when the burners go out.
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Old 12-14-2007, 02:55 PM   #5
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I used a small drill bit to check for blockage in the inducer. The drill bit goes in freely for more than an inch then feels like it hits something solid, is this normal? Should I try to force the drill bit in further, or am I only concerned with the opening? There isn't any blockage within the first inch, and I can feel the suction from the inducer when it is running. I just need to know if I should force the drill bit into the inducer.

Also, there are some new symptoms. Now sometimes the burners shut off as soon as they ignite, what could this be? It's not the flame sensor because I have cleaned it and the burners ignite and shut down at the same time. Could it be a gas valve problem?

Thanks for your help,
Mike
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Old 12-16-2007, 11:49 AM   #6
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If you get a code for the pressure switch why would you think it isn't the pressure switch? There is no connection to the high limit if the bruner isn't runnig. Isn't the high limit a manual reset in that you have to depress the red button to get it to reset? If the burners go on and off with in several seconds it is the flame rod in that it isn't sending current back to the control, the procelain maybe cracked, try changing the flame rod. Make sure you put the wires in the corect positions on the draft switch when you changed it.
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Old 12-16-2007, 01:11 PM   #7
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Do the flames roll out on start up? I have seen the rivets pop on the heat exchanger which is not a good thing. It can be ckecked but it can be difficult. A c/o reading would be nice too. If you think it is a limit you need to read voltage across the limit while its open. I think several of the limits are manual reset so there should only be one or two to check.

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