Goodman 3 Blinking Lights - Ongoing Issue


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Old 01-23-11, 11:45 AM
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Goodman 3 Blinking Lights - Ongoing Issue

Hi all - first post. I am not a professional (I'm sure that will become painfully evident as you continue reading). I have a 5 year old Goodman furnace. Beginning 2-3 years ago, the furnace will call for heat, but before the gas is ignited, the system will cycle down and report a 3 blinks diagnostic code. This is related to venting/pressure switch.

So I have literally had 6-7 service calls from trained professionals, and not a single one has been able to diagnose an issue with my furnace. Every one was able to get it running, but invariably within a few days it was deciding to not run. I have checked both incoming and outgoing PVC to ensure no blockages, both pressure switches have been diagnosed clean and operating normally. I've cleaned out drains (that didn't have anything in them). I've cleared the rubber tubes. Everything is checking out.

This final call, the serviceman decided to try something new: he unseated the incoming (2") PVC pipe fromt he top of the furnace. There's a 3-4 inch gap now that is allowing the furnace to pull air from my basement. The venting side was left as-is.

A few questions:
1) Is this safe? To reiterate, we're talking incoming, not venting. But can this create some sort of negative pressure situation if my basement is tight, and in turn pull exhaust down some other CO generating appliance (such as the hot water heater sitting right next to the furnace)? Any other risks?

2) This *seems* to have taken care of the issue. My furnace has run without issue for 4 days. And it's been relatively cold here (5 degrees F at night). Does this mean that perhaps the run on the incoming side is in some way faulty? I've checked the manual, and it indicates that either 2 or 3" pipe can be used. Should I replace with 3"?

3) Can pressure switches be impacted by cold? One of the pressure switches is installed just below the incoming pipe, and that air is very cold - obviously. Can pressure switches stick? I've read that issues like this rarely are the switch, but does it warrant my replacing it?

Thanks in advance for any input you may have.
 
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Old 01-23-11, 01:02 PM
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Removing the INCOMING pvc pipe that supplies combustion air to the furnace is not a hazard if the furnace isn't in a confined space such as a closet.

What should have been done is to use manometer to measure the pressure being applied to the pressure switch. If, for example, the correct pressure was being generated but the pressure switch wasn't closing, you'd know you had a problem with the pressure switch.

95% of the time the problem is with the furnace or venting system, not the pressure switch.

For example, your PVC pipe may be undersized, restricting the flow of air through the system and causing the pressure switch to open intermittently. What you have done by removing the incoming air supply pipe is to "installl" a larger air supply system!

If you have the installation manual check it to see the specifications for pipe size, length of run, elbows and vent termination.
 
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Old 01-23-11, 02:09 PM
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can the pressure switches be impacted by the cold? they can.....especially in cold climates. it wont hurt to disconnect the incoming pipe. if your house is a newer,fairly insulated house,I would not leave the pipe disconnected,as you need a certain amount of air infiltration for combustion air. are you positive that the manual said you can use 2 inch pipe? you must also check the length of the pipes,and then consult the manual for the maximum allowable distance.what model is it? how many btu's. you must also check the instructions very carefully on how the pipes terminate outside.you must check distances apart,elevation distances,etc,etc,they must be in the same pressure zone,as stated in the manual
 
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Old 01-23-11, 02:19 PM
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I just looked at a goodman manual,and there is a note that said you can use 3 inch pipe. did they use long sweep elbows? I think if you replace the incoming pipe with 3 inch now,and changed the exhaust when the weather breaks you would be ok.it must be borderline on the install. the other thing is that if it has not been cleaned on the interior of the secondary heat exchanger,(not the exterior),it may be a problem/
 
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Old 01-23-11, 04:27 PM
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Thanks for the replies. I'm fairly certain a manometer has been used by several techs, and the pressure switches have passed each time. I'm presuming the reason the latest tech didn't use the meter is because the furnace kicked on on its own 5 minutes before he arrived.

The interesting part is that, prior to modifiication noted, when I tried enough times or gave the furnace enough time, it would eventually cycle on and run. I can't pinpoint when or why, but this issue does seem to correlate to large temperature swings in December and January - which of course is when the furnace is working hardest. So it could just be that the increased frequency of failure is related to how often the furnace is trying to run. But again, this issue is intermittent as it is...

I will take a look at the measurements - I don't see wide elbows, though. They seem very tight to me - but I'm not a professional. The house is 5 years old.

Thanks for the advice.
 
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Old 01-23-11, 05:37 PM
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As far as I know, every manufacturer specifies long radius elbows. I agree with seabee570 on his suggestion to change to 3" pipe. I've encountered several furnaces, although within manufacturers accepted guidelines with 2", had problems like yours which when changed to 3" worked fine.
 
 

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