Payne furnace (1) keeps ticking (2) sometimes won't start at night

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Old 02-20-11, 12:33 PM
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Payne furnace (1) keeps ticking (2) sometimes won't start at night

I have an older Payne (model 396GAZ) that has two problems, probably connected: (1) the igniter keeps ticking even when the furnace is running, (2) the furnace sometimes will not come on, usually at night.

For problem #1, it goes through the regular heating cycle, it is just that the igniter keeps ticking, beginning when the tstat kicks in, main burners lighting and fan coming on, and continuing through until the tstat gets up to temp and the cycle ends.

For problem #2, the furnace will run fine for hours (and multiple normal cycles), then just won't come on. Thinking it was the tstat, we replaced the tstat, but it still happens. Happens most often at night (almost every night), and occasionally some days. To get it to start again, we turn the tstat to "off" mode, then back to "heat". It then starts up just fine.

In posts on various forums, it sounds like this is usually a flame sensor problems on most furnaces, but I don't see where to find it on this model, unless it is part of the pilot igniter assembly.

Any suggestions would be appreciated - it can get downright cold at night!

-Jeff
 
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Old 02-20-11, 01:04 PM
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Please confirm that your furnace has the 3 wire pilot burner ignition system. You will see some pilot tubing going to the pilot burner and a wire connector with three wires going to the pilot assembly, white, green and red wires if I'm remembering correctly.

There are two kinds of spark modules --- one about 2x3" in black plastic and the other about 4x6" or so in gray plastic. Which do you have?


Power for the spark goes through a SPDT switch on the pilot light/switch. When the pilot heats up it should shut off the spark and then switch on the power to light the main burner.

You shouldn't have both the main burner and the pilot switch sparking at the same time if the pilot switch is operating properly.

If you have an AC voltmeter, measure the AC voltage on terminal 5 of the electric gas valve, which is in parallel with the spark module voltage. You should see 24 VAC on that connection when the thermostat calls for heat and the spark starts. You should see the 24 VAC drop to zero at that terminal shortly before the main burner turns on, and the spark should shut off too.

#2----


Is the pilot light lit when the burners fail to light?
 
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Old 02-20-11, 01:38 PM
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SeattlePioneer - thanks for the quick response!

Yes, it has the three wire ignition, and the spark module is the black plastic version. The 3 wire pilot burner ignition system is probably 3-4 years old. I think that's the last time I replaced it.

I will need to dig out my multimeter to check the terminal 5 voltage, and will post back as soon as I do.

For #2, I don't know if the pilot light is lit, or if it even attempts to light. We don't know there's a problem until we notice it's colder than it should be, by which time everything is quiet. My impression is that it never starts to tick. We had that problem several years ago, so I'd probably notice ticking without the heat/fan not coming on. I'll see if I can catch it this evening as it cools down (with the sun shining it, the problem isn't likely to happen until then).
 
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Old 02-20-11, 02:20 PM
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Yes, you need to observe what is happening carefully.

#2 --- if the spark isn't functioning, the thermostat may not be calling for heat or something else is failing to switch on.

The black spark module will spark indefinite if energized and the pilot is not lit. There are conditions where the pilot will light but not the main burners.
 
 

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