furnace won't light then does

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Old 12-02-07, 07:45 PM
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furnace won't light then does

I have a Janitrol forced air natural gas furnace with the following problem. The furnace will start fairly normally with the induction fan starting and the ignitor beginning to glow - but it doesn't light. You can smell the gas. Then everything shuts down the ignitor, the gas, and the induction fan. After this the whole cycle begins again and then it lights properly and heats normally. I would not attempt to repair this myself, but I'm wondering what it is and how expensive its going to be? Any help appreciated.
 
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Old 12-03-07, 05:14 PM
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I WOULD try to repair this myself. This may be the perfect DIY furnace repair job, for at the DIY forum!

If you are lucky, your ignitor is simply weak. Even though it is glowing, it is not glowing quite enough to create the necessary combustion. The gas valve then opens and when it does not fire within a second or two, the furnace will retry up to 3 times and then give up. Often times after that happens, just the ventor motor will continue to run, and then you have to shut off the furnace to have it try this sequence again, to no avail.)

If you had a multitester (some people call then voltmeters), you coud test the resistance, in ohms, of the ignitor and determine if it was likely bad. Most hot surface ignitors (HSI's) are just held in by one screw and is a DIY job if there ever was one. The price of the ignitor may be in the $30 range, or somewhat higher if you get the better glo-stick variety which is univerasally adaptable.
 
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Old 12-03-07, 06:53 PM
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That's the odd bit last year I had the ignitor professionally replaced when the furnace was serviced. I never had this problem till the ignitor was replaced?!?

I know at the time it took the tech 2 tries to replace the ignitor apparently the first one was not the correct one.

Any other thoughts on what the problem has been. I've read some other posts that suggest the flame sensor - possible or no?
 
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Old 12-03-07, 07:16 PM
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If you actually had a flame started and then go out, it could be the flame sensor. However, you say that you are not getting a flame at all. Do you hear the gas valve open after the ignitor is glowing? If so, get one of those butane grille starters, and when the gas comes on, try to light the burners with the butane starter. If they light, the trouble is with the ignitor. Look at where it is located. It should be almost overlaping the edge of one of the burners.
 
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Old 12-03-07, 07:45 PM
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Originally Posted by mmbosman View Post
That's the odd bit last year I had the ignitor professionally replaced when the furnace was serviced. I never had this problem till the ignitor was replaced?!?

I know at the time it took the tech 2 tries to replace the ignitor apparently the first one was not the correct one.

Any other thoughts on what the problem has been. I've read some other posts that suggest the flame sensor - possible or no?
Long shot, but at one job i did another tech installed a ignitor and it turned out he didnt take the time to make sure it was in properly. in turn the ignitor was sitting to the side a bit and it was not allowing the gas to go to full combustion on ignition.

and goldstar is correct. if it was the flame sensor you would get fire but in about 3 seconds your gas valve would shut off. (rule of thumb)
 

Last edited by LaBait; 12-03-07 at 07:47 PM. Reason: adding notes
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Old 12-03-07, 08:28 PM
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There is definitely gas. The reason I know is because you can smell a bunch of it. That is the reason I started looking into the problem is because of this smell. Are there other reasons this could be happening?
 
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