My furnace won't start


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Old 10-31-20, 10:22 PM
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My furnace won't start

Hi all, I started another thread about replacing my furnace but would like to see if I can fix the current one first. It's a Carrier model # 58SX080-BC.

The pilot lights and then quickly goes out before the main burners can come on.

I've had something similar happen a few times in the past and replacing the 3 wire pilot burner has done the trick. This time, I've replaced it and no joy. Here's a video of the pilot through the view hole. https://photos.app.goo.gl/XSWfAm6oub7GsiZV7

The furnace has been working great for a couple of weeks. One thing that changed recently is that our roofers did a final clean up a few days ago and I saw them using a blower, blowing a bunch of dirt right near my furnace air intake. I don't know if it's an intake but it's pvc piping outside where I can always hear the fan before it lights. Not 100% sure it's related but that's when this started happening. Could dirt cause an issue if forced/blown in there? If so, what can I clean to resolve it?

If it's not dirt, what else can I check? Is it not getting enough gas to stay lit? I tried just using the pilot orifice from the new part in my old pilot burner first and that didn't do it, so I don't think the orifice is clogged.

I read about the pressure switch. I know where it is. Should I check it? How?

Thanks so much.
 
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Old 10-31-20, 10:35 PM
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That furnace is on the list of those affected by carriers class action lawsuit for heat exchanger problems. Could be something to do with the heat exchanger.
Check the pressure switch with your meter and see if it’s opening.
 
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Old 11-01-20, 09:19 AM
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That's an intermittent ignition system. It looks like the pilot flame is too small.
If it's not large enough..... it won't lock on and start the burner.

58SX manual (pdf)
 
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Old 11-02-20, 07:07 AM
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Probelm resolved

Thanks for the responses, guys. I sussed it out yesterday and it seems I was right about the roofers. I've cleared the plumbing outside and things seem to be back to normal...for now. I appreciate the responses. And I learned how to check my pressure switch.

I'm still on the other thread about replacing my system and the pros and cons of going with a heat pump vs gas. PJmax has been very helpful there as well. Replacing a gas furnace with an electric one. Thanks for the link to my manual as well.

Have a good week, all.
 
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Old 11-02-20, 02:05 PM
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Spoke too soon

Well this is embarrassing. Last night, the heat worked well, and lit fine this morning. But I now seem to have another, different problem altogether. For years I've battled the intermittent ignition that @PJmax mentioned but now it doesn't even attempt to start. In other words, I'm used to hearing the spark going "tick, tick, tick, tick..." until the pilot lights, or doesn't light. Now as the inducer fan motor is running, I have no sparking.. During the last incident, I tested the pressure switch and it is good.

What can I check that might not be letting it try to start?

Thanks again!
 
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Old 11-02-20, 03:46 PM
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What error code is being generated?
 
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Old 11-02-20, 03:57 PM
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The pressure switch must prove (close) before the ignition will start.
 
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Old 11-02-20, 04:51 PM
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roughneck77 If I'm not mistaken, this furnace does not generate error codes.
PJmax When the inducer motor is running, the pressure switch reads good, 29 volts on all 3 contacts.

What else then, after the pressure switch, tells the spark box to start sparking? How do I test the spark igniter box? I suppose the spark wire on the igniter electrode could be loose. I'll check that, but what is so difficult is that everything worked well this morning and then it didn't start again.
 
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Old 11-02-20, 05:06 PM
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This is not an easy furnace to work on. It's an early style ignition system.
Look on page 4 of the manual I linked to.
You need to follow the text description of operation thru the diagram.
 
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Old 11-02-20, 06:56 PM
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You should have 0 volts when checking across switches.
Don’t check to ground.
 
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Old 11-02-20, 07:10 PM
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That furnace uses a SPDT pressure switch. It needs to change state when the inducer starts up.
 
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Old 11-02-20, 07:39 PM
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Pressure switch

Confirmed. The pressure switch does change state with the inducer motor. The middle, raised contact goes from 0v to 28v when the motor turns on.
roughneck77 PJmax Thanks for the responses! Please stay with me. I'd like to keep this furnace going till I can get a new one installed later this month (fingers crossed). Getting quotes this week.

 
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Old 11-11-20, 08:21 AM
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Furnace is starting

Hi guys, just want to update you on this that you have helped me with.
Since I was getting no spark with the new 3 wire pilot, I decided to test the spark by re-installing the previous 3 wire pilot, and it sparked. So, I suppose, the NEW pilot was defective. Very frustrating.
My furnace has been starting as it should (thankfully) with the previous part in it which means to me that the theory of the roofers/cleaners blocking the PVC piping outside was correct.
I am still researching a replacement system as this one has got to be 40 years, or so, old.
Thanks again for your help. We are warm.
 
 

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