Jay in the Bay

Any HVAC experts? Furnace not igniting

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I found out the hard way during a cold weekend that my gas furnace isnt kicking on.  The fan turns on from the thermostat but shuts off after the furnace doesnt ignite. The gas line is open and the hot water heater and stove are getting gas.  

 

I opened the furnace and held down the "kill switch" button and the fan started, but the "OK" light blinks a sequence of two blinks, which the internet says signals an ignition problem.  The Orange "flame " light d doesnt turn on.

 

I have a call in for service but anyone familiar with what I'm talking about give me some insight at what might be going in so I can talk intelligently with the HVAC co and not get scammed?

 

Thanks!!!

Edited by Jay in the Bay

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on    an oil unit there is a cad cell relay that gets carbon/soot on it and won't let it run.  gas    has a thermocouple that can bite the dust.

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Try turning heater off at thermostat,then turn emergency shutoff switch(red wallplate)off for a couple minutes.  Turn back on,turn heat on at thermostat and observe igniter lighting up, your orange flame. See if this doesn't get your heater up and running.

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The little thermocouple thing is an easy fix. I have hit them with a nail file to just scrape off the crud and it has worked. If that works I’ll replace it. 

 

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1 hour ago, modelcitizen said:

Try turning heater off at thermostat,then turn emergency shutoff switch(red wallplate)off for a couple minutes.  Turn back on,turn heat on at thermostat and observe igniter lighting up, your orange flame. See if this doesn't get your heater up and running.

Just tried this.... no luck.  Thanks anyway!

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Done this for neighbor several times over course of 10 yrs. Gas,forced hot air,system is intertwined with her Vivent alarm system. Been "repaired" more than once but not fixed. "Resetting" like this has always gotten it up and running and runs interrupted for two years or so and acts up again. Symptoms exactly as you describe,thought may help your situation.

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Initial thought and, more than likely, a techs first move would be to replace the ignitor. How old is the unit and has the ignitor ever been replaced before? They do go bad. It's a $20 part and there's 2 screws and 2 wire nuts to replace it. Should take no more than 5 minutes to replace.

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On mine if you take the cover off there's a glass window you can see if the glow plug is working.

It also has a couple of clear tubes that go to what looks like a couple of diaphragms.

Once one tube had some water/condensate accumulated on a low spot that had to be cleared out to get it working again.

 

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Other than the thermocouple I've seen flue spill switches stop nat. gas from lighting. If there is a sensor in the flue above the unit, jump out the two wires to test it.

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23 hours ago, cheech said:

Other than the thermocouple I've seen flue spill switches stop nat. gas from lighting. If there is a sensor in the flue above the unit, jump out the two wires to test it.

I had a tech out yesterday look at it, and this seems to be it.  
The sensor apparently thinks the flue is closed and not igniting, but tech examined it and saw it was open.  He's going to replace it today.

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I was going to suggest a flame sensor. Mine was fouled up last year. Cleaned it with a light sandpaper and it's been working fine. I keep a spare for when it craps out completely. That sensor should be cleaned frequently, btw. 

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