Carrier 58SSB ignition problems


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Old 03-31-09, 08:26 AM
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Carrier 58SSB ignition problems

My furnace is a Carrier 58SSB, about 20 years old. For the past 10 days it's been having ignition issues that seem to be getting worse over time (it still often works just fine, but that's getting less common). The inducer motor kicks in, the pilot lights quickly, but then after a few seconds it sounds like a relay or transformer tries to kick in and the pilot goes out.

Every once in a while the pilot will stay lit and the burners will light successfully, and the blower is fine. Usually it runs just fine from this point, though a couple times I've seen the burners shut off after 10-15 seconds and the cycle starts over. A couple times the burners even sounded like they were struggling to get enough gas, like you would imagine how it would sound if there was air in the gas line, though I don't think that's the issue.

From what I have read it sounds like this may be the valve? I have a multimeter and a schematic for the furnace but I'm not sure what lines to measure voltage across. If it's a transformer or relay on the valve, is that replaceable? Or do I need to replace the whole valve as a unit?

I almost feel silly even mentioning this, but coincidentally these issues started the very same morning that Questar began digging up our street to replace the neighborhood's old 1950s gas line. I can't think of how that'd be related to the issue though.
 
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Old 03-31-09, 11:15 AM
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Probably the pressure switch is opening, which will shut off the pilot light.

Measure the voltage from terminal 4 on the gas valve to ground. You should see 24 vac at that terminal after the inducer motor starts up, and it should stay on until the thermostat shuts the furnace off.

What I'm expecting you will see is that voltage shutting off when the pilot light goes out.
 
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Old 04-01-09, 12:46 PM
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Thanks for the help SeattlePioneer, I actually saw the voltage continue at 24v after the pilot goes out, though.

However I realized that I still have a few weeks left on the home warranty that my realtor bought us and we've never used, so I had them send a guy out. He confirmed the valve was dying, replaced the entire valve and all is right again.

You appreciate your heater a lot more after spending 2 days without it.
 
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Old 04-01-09, 07:11 PM
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Was the pilot cycling on every 15-20 seconds after that pattern started, or was it a significantly longer cycle? That kind of short cycling is the classic symptom of a burned out hold coil on the gas valve. From what you wrote, I was presuming the pilot was staying on for a longer period.


Anyway, glad you got it fixed.
 
 

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