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  #1  
Old 10-24-2012, 11:50 AM
baileygrrrl baileygrrrl is offline
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Gas furnace starts...then stops

Problem started a few days ago. I hear the sound of the furnace starting up, but before the blower comes on, it just stops. It does this every few minutes. I turned the unit off today because I worried about leaving it to do that while I was at work.

Any idea what can be wrong? My husband thought it might be an airflow issue and changed the furnace filter and checked to make sure nothing was blocking the intake vents. Problem still exists. He's convinced he can figure this out on his own but with 2 kids in the house and some pretty cold weather on it's way, I'm convinced we need to call the professionals.
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  #2  
Old 10-24-2012, 11:51 AM
Thudlow Boink Thudlow Boink is offline
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Is the pilot light lit?
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  #3  
Old 10-24-2012, 12:00 PM
TriPolar TriPolar is offline
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Pilot out. Gas turned off (or empty if you have tanks). Clogged air intake or chimney. Sounds mostly like no gas. Could be a broken thermocouple or other type of sensor.
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  #4  
Old 10-24-2012, 12:02 PM
Rachellelogram Rachellelogram is online now
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I'd check the pilot light first thing. Same thing happened to the gas furnace in the home I'm renting.
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  #5  
Old 10-24-2012, 12:04 PM
baileygrrrl baileygrrrl is offline
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Thanks, I will have my husband check. He's far from a handyman so I hope this is a simple task!
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  #6  
Old 10-24-2012, 12:08 PM
ftg ftg is offline
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I went thru this last winter. The igniter glows, the gas kicks on, the burners fire up ... and then it all shuts down.

There's usually a blinking code visible thru a peep hole that you can look up to see what the problem might be. Lots of possibilities. Bad sensors, lose wires, etc. In my case, the control board was going bad. I could have saved some money and done it myself but I had the HVAC guy do it.

Some time earlier I had a problem where the fan continued running and it was a high-low sensor which was easy to swap out. That part can also cause premature shutdown problems, IIRC.

There's several forums that specialize in home DIY things, including ones for HVAC pros. (You can't post, but you can search them at least via Google.) Look up your model and any codes.
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  #7  
Old 10-24-2012, 12:15 PM
engineer_comp_geek engineer_comp_geek is offline
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Could be a bad flame sensor.

Here's a youtube video showing how to check it.
http://www.youtube.com/watch?v=I86joWL66aE

As ftg said though it could be other things. There are plenty of youtube videos showing you how to test various parts.
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  #8  
Old 10-24-2012, 12:15 PM
Machine Elf Machine Elf is offline
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Quote:
Originally Posted by baileygrrrl View Post
Problem started a few days ago. I hear the sound of the furnace starting up, but before the blower comes on, it just stops. It does this every few minutes. I turned the unit off today because I worried about leaving it to do that while I was at work.
There are a few safety devices that have to "greenlight" before a residential gas furnace will deliver heat. Once the thermostat in your living room tells the furnace "we need heat, " the whole sequence goes something like this:


1. Furnace's controller sends power to the flue (exhaust) gas blower.

2. Controller looks for signal from damper that indicates the flue gas blower is indeed working. If no signal, the process shuts down. If there is a signal, the controller allows blower to run for ~30 seconds (to clear out any natural gas that may have leaked into the burner since the last burn), and then proceeds to step 3.

3. Controller turns on power to the gas ignitor. Usually this is a hot-surface ignitor, a little toaster element that glows red hot.

4. Once the ignitor is hot (10 seconds), the controller opens main gas valve. If the ignitor is working, then the gas ignites, and you hear the burners roaring away. At this point the controller is looking for a signal from the flame detector, which would indicate successful ignition. If there's no signal within a few seconds after opening the main gas valve, the controller assumes the burners aren't lit, and it shuts the main gas valve and aborts the whole process. If there is a signal, then the controller figures the burners are lit, and after a ~30-second preheat, it will turn on the main house blower and start delivering heat.

If no signal in #4, then the controller will try again in a few minutes. After several unsuccessful attempts, it will usually stop trying.

I've had problems in the past with the burners getting shut off in step #4 due to a "no flame detected" condition. This is usually caused by one of two things:

1. bad ignitor. They'll only take so many heat cycles before they crack. If you pull the inspection panel off of your furnace and see that the burners really aren't lighting, look around for that igniter (something like this) somewhere near the burners; if it's cracked, it'll probably be obvious. Take it out, call an appliance parts vendor, and see if they have it in stock. When installing the new one, do not touch the ignitor element; your skin oils will result in premature failure.

2. bad flame sensor. If (while you watch) the burners light up and then shut down a few seconds later, then the ignitor is fine, but your flame sensor ain't happy. Often times you can fix this by cleaning them. Try scrubbing it with steel wool or some other fine abrasive, and then reinstalling.

Last edited by Machine Elf; 10-24-2012 at 12:15 PM..
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  #9  
Old 10-24-2012, 12:35 PM
baileygrrrl baileygrrrl is offline
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Thanks for all of the replies. One thing for sure, I am not going to solve this from my office chair

I'll have my husband do a more detailed look tonight. Thank doG for youtube videos and the like. We may not be able to fix it, but at least we might be able to diagnose the problem.
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  #10  
Old 10-24-2012, 12:40 PM
AllShookDown AllShookDown is offline
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My furnace was doing the same thing a few weeks ago. The furnace guys replaced the control board and all is well. They said it had probably gotten fried in a power surge.
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  #11  
Old 10-24-2012, 02:05 PM
jasg jasg is offline
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First and cheapest, change filters. If filters are very dirty, the combustion chamber can overheat and the limit switch will kick in and turn the heater off.
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  #12  
Old 10-24-2012, 02:05 PM
Kimballkid Kimballkid is offline
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Quote:
Originally Posted by ftg View Post
There's usually a blinking code visible thru a peep hole that you can look up to see what the problem might be.
Depends on how new it is. If it's more than a few years old, it may not have anything that will display a code.
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  #13  
Old 10-24-2012, 02:17 PM
Seanette Seanette is offline
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I'm siding with "call a professional", on safety grounds. I also hope you have a working CO detector.
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  #14  
Old 10-24-2012, 02:21 PM
Folly Folly is offline
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Quote:
Originally Posted by engineer_comp_geek View Post
Could be a bad flame sensor.
This was my guess just from the thread title.

The part of the sensor extending into the flame is basically just a bar of metal. I was able to fix mine just by sanding off the oxidation/corrosion buildup or whatever the heck the build up was.
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  #15  
Old 10-24-2012, 02:31 PM
Folly Folly is offline
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In fact here's me asking a similar question in 2007.
http://boards.straightdope.com/sdmb/...d.php?t=404867
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  #16  
Old 10-24-2012, 02:32 PM
Machine Elf Machine Elf is offline
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Quote:
Originally Posted by Seanette View Post
I'm siding with "call a professional", on safety grounds. I also hope you have a working CO detector.
Ignitors and flame detectors are easy-to-service items that don't present any particular danger to a homeowner who knows how to use a screwdriver and a circuit breaker.

A particularly smart homeowner will have a spare ignitor handy so that when the in-use one breaks at 9:00 on a Saturday night in January, he doesn't have to wait 36 icy hours to buy a replacement.

As for the CO detector, I concur. Furnace heat exchangers crack and chimneys get blocked from time to time, and as insidious as CO poisoning is, no home should be without a detector.

Last edited by Machine Elf; 10-24-2012 at 02:33 PM..
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  #17  
Old 10-24-2012, 03:08 PM
johnpost johnpost is online now
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Quote:
Originally Posted by Seanette View Post
I'm siding with "call a professional", on safety grounds. I also hope you have a working CO detector.
should have one outside of each bedroom area. also having one near fuel burning heater/boiler/furnaces is good.
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  #18  
Old 10-24-2012, 08:38 PM
ZipperJJ ZipperJJ is online now
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Quote:
Originally Posted by engineer_comp_geek View Post
Could be a bad flame sensor.

Here's a youtube video showing how to check it.
http://www.youtube.com/watch?v=I86joWL66aE

As ftg said though it could be other things. There are plenty of youtube videos showing you how to test various parts.
Do this cuz it's free and easy. I do mine once a year now that I know how to do it and it's solved my problem every year so far.

If that doesn't work then call The Man. But don't pay The Man to clean your flame sensor!

I had a cracked somethingorother one year, and the crack would not be a problem until it expanded too much from heat at which point a vacuum was unsealed.
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  #19  
Old 10-25-2012, 10:40 PM
Tamex Tamex is offline
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Originally Posted by ZipperJJ View Post
Do this cuz it's free and easy. I do mine once a year now that I know how to do it and it's solved my problem every year so far.

If that doesn't work then call The Man. But don't pay The Man to clean your flame sensor!
This. We've had this very problem, and it's always been the flame sensor. Had to call The Man to fix it once (in the middle of winter, of course!) but after that, my husband has always cleaned it himself.
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  #20  
Old 01-15-2014, 08:00 AM
c46443 c46443 is offline
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One last possible solutin

Before calling out a repairperson, after you have checked the pilot light, cleaned the flame detector and all the wire connections, the last item to check would be the small air hose lines that sense the air flow in the furnace. Unplug each end and check for dust clogs anywhere. I used a wet vac to suck out all the dust when my furnace had the same problem and fixed the furnace. The last and most expensive is replacing the control board.
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  #21  
Old 01-15-2014, 08:32 AM
DCnDC DCnDC is offline
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Check the date on the OP. It's been well over a year. Hopefully her problem has been fixed by now.
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  #22  
Old 01-15-2014, 09:13 AM
Amateur Barbarian Amateur Barbarian is online now
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All of the above is true, but I've also had gas furnaces do this short-cycle thing when the thermostat did not have an adequate temperature hysteresis - there should be a degree or more between the temp it turns on and the temp it turns off. If the band is too narrow, it will jitter between on and off until the house temp drops another degree or so. The test is to force the furnace on by turning the thermostat up several degrees - if the furnace kicks on and runs fine, replace the thermostat.

Last edited by Amateur Barbarian; 01-15-2014 at 09:13 AM..
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  #23  
Old 02-06-2014, 06:22 PM
andrewclaus andrewclaus is offline
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Similar furnace lighting problem

I thought I'd piggyback on this old thread with a similar problem. I have a cheap Goodman furnace in a rental house that just had an ignitor fail. I replaced the ignitor and now I notice it takes two cycles to fire. The new ignitor glows just fine, but only for a second or two before the gas valve opens. The first time it doesn't light and shuts down. The second cycle, the same thing happens but the burners ignite. I thought the ignitor was supposed to glow for much longer before the gas valve turns on.

I don't know if this was happening before the ignitor replacement. Could it have anything to do with that? Is there an adjustment for this, should I get a new control board, or any other ideas?

Thank you. This is my first post here and I'm impressed with the replies above.
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