Goodman Furnace Not Igniting

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Old 02-28-13, 11:21 PM
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Goodman Furnace Not Igniting

Hi:

I have a Goodman GMT-115-5A Furnace. A little over a week ago, my vent fan died (it was clicking, but wouldn't spin on it's own and of course nothing else would happen in the ignition cycle). I replaced that part -- things worked fine for a day or two...now a (maybe) new problem has cropped up further into the ignition cycle.

Now, the thermostat calls for heat, the vent fan kicks on, after a few seconds the ignitor starts to glow -- but then no gas is released and, obviously not flame starts. The system then turns the ignitor off, waits a bit, tries a couple more times and then shuts down with a "one" blinking light code.

I shut the thermostat down, it was Sunday afternoon...and then Monday morning, before I called a tech, I decided to try to start it up again -- and sure enough the dang thing fired up. But then sometime before we woke up Tuesday morning, the problem cropped back up and the furnace wouldn't fire.

Tonight, I used some fine steel wool to clean up the flame sensor. That doesn't seem to have done anything. Still have the problem.

Any idea what I should check next? Could I have done something wrong when I replaced the vent fan? Could it be the gas valve? Thanks for any help you give!

~Dave
 
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Old 03-01-13, 01:23 AM
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Welcome to the forums.

The vent fan is not your problem. If the vent fan were at fault the ignitor would not come on.
It's not the flame sensor either. That sensor is only active after burner lights.

One flash of the LED means ignition failure. In your case it's going to be the control box or gas valve.
It's going to take a meter to check for voltages.

Do you have one and do you know how to use it ?

The link to your furnaces service manual. Go down to page 33 on for servicing info.
http://www.hvacpartsshop.com/Gmph075-4 Series.Pdf
 
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Old 03-01-13, 08:51 AM
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Thanks PJ -- I do have a pretty good multi-meter and I guess an average knowledge of how to use it

I pulled the wires off the valve (because I couldn't figure out how to contact both terminals around the plastic coating otherwise) -- and measured the voltage across those two wires -- it consistently measured around 2 volts when it wasn't trying to ignite and then jumped to about 27 when the click happened that would normally be the gas turning on -- and back down to 2 after the igniter stopped glowing. So, based on the what you said and what I read in the manual -- that seems to indicate I've got a bad valve.

(BTW, is there a better/correct way to measure the voltage on the valve without removing the wires?)

~Dave
 
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Old 03-01-13, 08:56 AM
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On the surface that would appear correct. However the gas valve presents a load to the control board and an intermittent connection in there could cause the same problem.

Can you reconnect the gas valve and check the wires at the control board ?
Then if you see the same thing your gas valve is indeed defective.

I would hate to see you change the gas valve only to find an intermittent connection.
 
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