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Old 12-15-2009, 02:09 PM   #1
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intermittent problem--furnace won't light


Have a Gibson, high-efficiency, Model KG6C060C-12 gas furnace. I've had an intermittent (once a month, once every six months) problem. The pre-fire fan comes on, and glow-plug lights, but when the time for the burner to fire, the gas valve clicks, the burner does not fire, and the start-up cycle starts again. The circuit indicator light blinks 3 times, repeatedly (the error list says this means, "Pressure switch stuck closed.").

I've had the service company out four times (unfortunately, they send a kid with limited diagnostic skills). He changes parts: first time, cleaned burner; second time, changed valve; third time, taped loose wires; and now the fourth time, wants to replace the circuit board--to the tune of $300.

The frustrating part is: when he leaves, it seems to be fixed--sometimes for months!

I've asked, now three times, that if the blinking error light says the pressure switch is stuck, should we not replace what appears to be an intermittently sticky pressure switch? I'm told that that error code can mean many different problems.

I've repaired computers and it's been my experience that, generally speaking, hardware problems are consistent, software problems are intermittent--if the environment doesn't change (temperature, humidity, etc.) circuit boards tend to react consistently.

One last observation, then I'll actually ask my question. Today I noticed that the hose that runs from the pressure switch to the valve is routed so that it has to be stretched to fit the nipple on the valve, just barely reaching. I looked at the end of the hose and it was hardened and elongated out-of-round, almost loose. I rerouted the hose and cut off the 1/2 inch of the hose that was mis-shapened. Now it fits snugly, without being stretched. Since the hose is right in the middle, it always gets bumped or moved during any repair. This might explain why it works after the repairman leaves--for a while.

SO, my two questions: 1) Should I consider replacing the pressure switch before replacing a circuit board? 2) Could a loose pressure-switch-to-valve hose cause this problem?

Thanks a bunch.

Dave

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Old 12-15-2009, 02:11 PM   #2
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intermittent problem--furnace won't light


I should add...the furnace is working fine, for now...
Dave

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Old 12-15-2009, 02:15 PM   #3
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intermittent problem--furnace won't light


If you can't somehow induce the fault, you could rent or make an Event Recorder; it triggers on the fault and reads back data from many test points on what was happening just before the fault occurred.

If a service call is $X, and a part costs $Y, you should replace it if the chance of the part fixing the problem is at least 100Y/X.
E.g., $50 service call, $20 part, replace if the chance is at least 40%.
The HVAC guys on this forum can/will/may/won't(?) give you the likelihood, in your particular case.

Last edited by Yoyizit; 12-15-2009 at 02:20 PM.
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Old 12-15-2009, 02:18 PM   #4
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intermittent problem--furnace won't light


Cool. I didn't know that such a thing existed...Event Recorder, eh?

Thanks.
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Old 12-15-2009, 02:21 PM   #5
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intermittent problem--furnace won't light


Those are both wonderful generic answers, but what about my specific questions? Could the pressure switch be the problem? Could the loose hose be the problem?

Thanks.

Dave
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Old 12-15-2009, 02:24 PM   #6
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intermittent problem--furnace won't light


Quote:
Originally Posted by dwwomack View Post
Those are both wonderful generic answers, but what about my specific questions? Could the pressure switch be the problem? Could the loose hose be the problem?

Thanks.

Dave
Ask HVAClover; since he is a member of "The Undead" he probably has insights that we ordinary mortals don't have!
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Old 12-15-2009, 02:32 PM   #7
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intermittent problem--furnace won't light


Okay...
...thanks.

Dave
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Old 12-15-2009, 04:07 PM   #8
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intermittent problem--furnace won't light


Loose hose could cause pressure switch fail to close but not stick closed. Fault code should be ignition failure after that sequence, not pressure switch closed. Intermittent board problems are common, probably what you have going on.
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Old 12-15-2009, 04:12 PM   #9
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intermittent problem--furnace won't light


Could be bad pressure switch. Or moisture in the hose.
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Old 12-16-2009, 12:43 PM   #10
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intermittent problem--furnace won't light


Curious as to why when the error message stated that a switch was faulty why it was not replaced during any of the service calls.
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Old 12-16-2009, 01:26 PM   #11
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intermittent problem--furnace won't light


A pressure switch error. Seldom indicates a bad pressure switch.
Only tells you it didn't open or close when it should have. Its up to the tech to determine cause.

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