Anyone know anything about gas furnaces?

We've been having some issues with our gas furnace. Most times when the thermostat goes below its target temp turning the furnace on, but the burner doesn't light. Thhe ignitor heats up tries to light the burner, but instead of it lighting it just shuts the gas off. Then just blows cold air through the system for a few minutes, shuts off and it tries to light again. Sometimes going through this cycle 3 or 4 times before finally lighting.

The furnace is 13 years old, and uses a hot surface ignitor. The thermostat we use is programmable. We just bought the house, so we have no idea of what has been replaced, or if the other owners were even having problems with it.

Sounds like the ignitor is failing. There is obviously gas in the system...cause it finally lights.

There also could be the possibility of a carbon build up at the ignitor. The build up prevents the ignition of the gas--and it take a few times for the carbon to heat up enough for the gas to light...

I'm thinking of one of two issues. If the furnace does not light the gas or the gas does not even start to flow, a bad gas valve could be the issue. As long as the igniter is glowing red it is not the problem. If the furnace does light but shuts off very soon after, clean your flame sensor. I actually do this once every year because being in the north our furnace gets a lot of use. I would try to clean your flame sensor and make sure you have a clean filter in there. To clean it use very fine sandpaper, scotch bright, or steel wool. Also your furnace might have a diagnostic trouble light in it. Take a look around. Hope this helps. Vince

Standing pilot or electronic ignition? Sounds like the thermocouple or flame sensor is going out. You can try and clean it up with fine sand paper or emory cloth if you have it. I would replace it with a new one ASAP, you don't want to get caught without your heater when you really need it! Google Johnstone supply in your area... they should have what you need for cheaper and just do it yourself for about $30 instead of paying someone $230 to do it. Post up in here if you need help walking you thru the changeout.

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Originally Posted by Vince @ FLT

I'm thinking of one of two issues. If the furnace does not light the gas or the gas does not even start to flow, a bad gas valve could be the issue. As long as the igniter is glowing red it is not the problem. If the furnace does light but shuts off very soon after, clean your flame sensor. I actually do this once every year because being in the north our furnace gets a lot of use. I would try to clean your flame sensor and make sure you have a clean filter in there. To clean it use very fine sandpaper, scotch bright, or steel wool. Also your furnace might have a diagnostic trouble light in it. Take a look around. Hope this helps. Vince

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+1

Look for a blacken round rod about 3/16" in dia. about 2" long. It should be shiny. It has a wire on the base end going to the control box. It generates current from the flame, if it is dirty it does not send current so the control thinks there is no flame and shut off the gas.

:twocents:

Like people have said if your ignitor is glowing red when the heater starts and the gas valve is not lighting then i would say the gas valve is sticking. Some times comes on some times wont. (i just had on do this last week and the valve would some times work and some times not.) Next time it does it try and tap on the valve and see if it starts. If it does then replace the gas valve. If it does not seem to work when tapping then check when the ignitor is glowing and see if you get 24volt to your gas valve if you do and the valve is not opening then replace the valve. Most gas valve run around $50 to $100. Either take it off and take it someone and get a new one or right the model number down and get a new one. If you dont have 24volts then back trace it and see if all your safety's are closed and not opened most of them should om out closed with a tone. If you need any other help let me know.


If the flames are lighting for and little bit and then shutting off then like others were posting the flame sensor is either dirty or going bad.

I'm posting up a vid. After looking I'm not seeing a rod that would look like it is just for a flame sensor. But the ignitor looks like it could be the sensor. The first few seconds of the vid, you can't see it but the gas for the ignitor is on.

http://i702.photobucket.com/albums/w...h_DSCF0637.jpg

flame sensor
It has to be your flame sensor. Can you clean the two circular thing a bops that are on the left and right? Maybe thats the flame sensor. I have never seen them before.

Keep warm

The round things are flame roll out switchs/ high temp switchs if they get two hot it shuts the gas off to the gas vavle. Now it almost looks like when it first trys to start the gas valve is not putting enough gas out to light all three burners. Have you tried to hit the gas valve when the first one is burning. If it was a flame sensor then all three burners would come on and then go off a little while later.

Also check for me if when it does this check the 24volts to it.

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Originally Posted by hunt4game29

The round things are flame roll out switchs/ high temp switchs if they get two hot it shuts the gas off to the gas vavle. Now it almost looks like when it first trys to start the gas valve is not putting enough gas out to light all three burners. Have you tried to hit the gas valve when the first one is burning. If it was a flame sensor then all three burners would come on and then go off a little while later.

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Cool :doofus:

:imwstupid:

I tried tapping the valve, and that didn't do anything. Then got the multimeter out.. and well my fuse is bad in it. I'll get one tomorrow and check. If that checks out, does that pretty much the valve could be bad?

Yeah check to see if you have 24 volts when its messing up. If it does i would say its the valve but i hate to tell you it is with out seeing it in person and then it not be. But when i have seen others heaters act kinda like this its been the gas valve. But its hard to say with all the other things some heater have and some dont as far as saftys and what not.

So check the 24 volts before its on when it starts ect. It should have it a little bit after the ignitor starts to glow. See if you lose it when the gas stops or what. Thanks matt

Sorry I didn't check in yesterday, as soon as I saw your video I knew what your problem is. The burners are dirty. You need to take them out and blow them out with compressed air, problem fixed.
At the flame end of the burners, where they are screwed down and connected together, with the wing-shaped stamping, is a channel for the flame to travel from burner to burner. There is either a cobweb in there, or dryer lint. After you fix the furnace, check to see if your clothes dryer exhaust is clogged.
This is my job, your problem is very common.
Oh, yeah: if there is a flame rod, it is always a good idea to give it a swipe with sandpaper. Scotchbrite is only OK if you are sure the rod is cold, it can melt and ruin the flame rod. If you don't have a flame rod, the ignitor can be the sensor in some systems. I think you do have a flame rod, because if the ignitor was the sensor, it should stay running with that right hand burner firing, and I think I see it behind the left burner.
If the ignitor is the sensor, then you have dirty burners and a bad ignition module.

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Originally Posted by hunt4game29

Yeah check to see if you have 24 volts when its messing up. If it does i would say its the valve but i hate to tell you it is with out seeing it in person and then it not be. But when i have seen others heaters act kinda like this its been the gas valve. But its hard to say with all the other things some heater have and some dont as far as saftys and what not.

So check the 24 volts before its on when it starts ect. It should have it a little bit after the ignitor starts to glow. See if you lose it when the gas stops or what. Thanks matt

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Still have to get a fuse for my tester. So haven't tested that yet. But will.

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Originally Posted by MikeGyver

Sorry I didn't check in yesterday, as soon as I saw your video I knew what your problem is. The burners are dirty. You need to take them out and blow them out with compressed air, problem fixed.
At the flame end of the burners, where they are screwed down and connected together, with the wing-shaped stamping, is a channel for the flame to travel from burner to burner. There is either a cobweb in there, or dryer lint. After you fix the furnace, check to see if your clothes dryer exhaust is clogged.
This is my job, your problem is very common.
Oh, yeah: if there is a flame rod, it is always a good idea to give it a swipe with sandpaper. Scotchbrite is only OK if you are sure the rod is cold, it can melt and ruin the flame rod. If you don't have a flame rod, the ignitor can be the sensor in some systems. I think you do have a flame rod, because if the ignitor was the sensor, it should stay running with that right hand burner firing, and I think I see it behind the left burner.
If the ignitor is the sensor, then you have dirty burners and a bad ignition module.

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As far as the dust or something in the burners, I caught it when the furnace was coming on. Of course it didn't come on, so I blew through the burners, and tapped on them pretty hard, when it tried to light again it did, but I can't tell if it was from dust or if it was just working right the second time. And I saw the sensor on the left burner tube, pulled it out.. and well its been sanded before, and it has a pretty big brownish spot on it.

http://farm4.static.flickr.com/3324/...490748bd50.jpg
http://farm4.static.flickr.com/3450/...b600a75c14.jpg

Sanded it off. See how that goes, and when I get home I'll pull those burner tubes out and makesure those are clean. And I'll test the valve for 24v too.

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Originally Posted by mnc2fan

...As far as the dust or something in the burners, I caught it when the furnace was coming on...and tapped on them pretty hard...

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If I could fix furnaces over the internet I would get stuck to the couch. (Home sick today) I as going by what I saw in the video, my diagnosis is still the first thing that I would check, but your banging on stuff and getting intermittant lighting makes me think gas valve, as hunt4 said. If when the right burner lights, and you are holding a lit propane torch pointing at where the flame should be in the middle burner, and it lights, I would still suspect dirty burners.
Your flame rod is fine.

It does get 24v to the valve, when it tries to light, something cuts the 24v and the gas cuts off. I do appreciate the help. Its given me lots of things to try.

Something else. What happens if the intake for the furnace is too small? I think I just answered that, the furnace intake is 16x25, the actual hole for the intake is 8x25. Any thoughts on that? Its a 60k btu unit.

How can you go this long without a furnace?
After watching your video again, I am going back to my dirt answer.
What you will notice with not enough return (intake) air is the flames will light normally and run for awhile. In anywhere from a couple to several minutes, the flames will shut off even though the thermostat isn't satisfied. The blower will remain running like it normally does after the flames shut off, except after a few minutes the ignition cycle will start again. It is normal for the blower to stop at the start of each ignition cycle, so that is not an indicator. The only way you can be sure that the thermostat has not reached setpoint when the flames go out is to test across the "R" and the "W" low voltage terminals. If your meter shows no voltage, the thermostat is still calling. If you have voltage from terminal to terminal, the thermostat is satisfied.
There is a limit switch that senses the air temperature downstream of the burners. When the switch gets too hot because of a lack of airflow, it kills the burners and keeps the blower running until it cools off and the cycle starts again.
If this is happening to your furnace, it is a seperate issue from what is happening in your video.

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Originally Posted by MikeGyver

How can you go this long without a furnace?
After watching your video again, I am going back to my dirt answer.
What you will notice with not enough return (intake) air is the flames will light normally and run for awhile. In anywhere from a couple to several minutes, the flames will shut off even though the thermostat isn't satisfied. The blower will remain running like it normally does after the flames shut off, except after a few minutes the ignition cycle will start again. It is normal for the blower to stop at the start of each ignition cycle, so that is not an indicator. The only way you can be sure that the thermostat has not reached setpoint when the flames go out is to test across the "R" and the "W" low voltage terminals. If your meter shows no voltage, the thermostat is still calling. If you have voltage from terminal to terminal, the thermostat is satisfied.
There is a limit switch that senses the air temperature downstream of the burners. When the switch gets too hot because of a lack of airflow, it kills the burners and keeps the blower running until it cools off and the cycle starts again.
If this is happening to your furnace, it is a seperate issue from what is happening in your video.

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It works, just takes it a few tries to get it to come on. No its not doing anything like that, only issue I know of is whats in the video. I'm agreeing on dust or dirt, I'll attack that in the morning, pulling out the burner and cleaning them.

Hope cleaning works. Let us know if it does not.

Also what state do you live in. I am guessing up north some where from the snow pics.

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Originally Posted by hunt4game29

Hope cleaning works. Let us know if it does not.

Also what state do you live in. I am guessing up north some where from the snow pics.

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Yes it work beautifully! It had lots of dust caked in the tubes. But didn't really look like it could cause an issue. Put all back together, turned it on, and the first time the ignitor glowed the gas went through all three tubes and light without an issue. Washington state, but was the state of confusion with the furnace. Thanks for you help!