Heil furnace igniter/flame senosor question. TIA


Greetings all,
I have a Heil furnace that has a problem. I was hoping that someone here could help me out.
The problem is the igniter sparks and lights the pilot and then the pilot goes out right away. I spoke w/ a friend who is a HVAC tech and he told me that it was most likely the flame sensor. Ok so I took the unit apart and removed the igniter assy looking for a flame sensor. I couldn't find one. The closest I can figure is that the igniter and flame sensor are one and the same.
After I took the whole assembly out and cleaned it up per my friend's instructions, it still didn't work. I used a fine emery cloth and followed up by spraying the assembly w/ Zep Elec contact cleaner to make sure I flushed away any particles I may have created by sanding.
Tonight I turned the igniter 90 degrees in it's mount and voila, the pilot stayed on for more than a second and the burners fired up.
The igniter unit has what appears to be a high tension lead going from the end of it to a box made by Honeywell. There is also a grey ground wire coming from the unit's mounting bracket that goes to the "ground" terminal on the same box. That doesn't really make sense as the furnace should be grounded anyway but that may there just for redundancy.
The furnace was installed in 1992 or 1993. I don't know the exact model of the furnace but in doing some research, I found a picture of the igniter assembly online. It can be viewed here:
http://www.expertappliance.com/heil-heating.html
It is about 1/3 of the way down the page and is called a "Pilot Igniter Sensor"
The only way I can figure is that the Honeywell box sends out a high voltage to the unit in order to fire the spark, and then waits for a signal coming back on the same line telling the microprocessor that the flame is present and it is okay to fire the secondary part of the gas valve. The valve has three wires going to it and I figure that it must be a two stage valve that fires the pilot at the first stage and the burners at the second.
My questions is this. Is there any way other than just swapping parts to determine whether it is the igniter/flame sensor assembly or the Honeywell box causing me grief?
Any answers would be greatly appreciated.
Thanks in advance,
EBB
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Dick wrote:

You're correct on all counts.
Do a GOOGLE for: Flame Rectification for how they sense the flame.
It would take a very specific tester to check sensor properties. Much easier to swap them out.
Jim
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Thanks guys. I just posted earlier today about an issue with a Coleman furnace. I've had to replace the ignitor 2 or 3 times in 10 years. I replaced them often enough that I bought a spare. I'd talked to 2 HVAC guys that were looking everywhere but at the ignitor/sensor. I had bypassed switches, replaced a thermostat, and was banging my head against a wall.
After reading your Heil question, I thought maybe the sensor is bad even though the ignitor hasn't burned out. It was worth a shot. So after reading your post...I now have heat. Thanks for setting a lightbulb off in my head.
Michael H.

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I saw where you also posted this on the alt.hvac group. It's funny because I posted my problem there today as well. I got treated the same as you, which was pretty rough.
I was caught off-guard, as I've never been treated that way on any usenet group, and found it quite surprising. You would think you were wrecking the HVAC profession as personal as they take it. The one poster (bu** sh&&, or something close to that) is a major jerk.
Anyway, good luck, and thanks for getting me on the right path.

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The control box is looking for a DC signal from the sensor. The sensor is the one with the HV lead going to it. Make sure the unit is properly grounded, (fusebox,ignitor. If the unit still won't work, you may have to replace the grey control box.On 23 Apr 2005 13:08:02

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Now the grey control box is doing nothing. The relays stopped clicking and everything. I'm going to replace the control box and the igniter/sensor tomorrow. The sensor is only around $25 but the box is gonna be pretty expensive.
I found a supply house online that happens to be a mile or so from me and their pricing is quite fair.
One thing perplexes me though. When I turn off the gas at the solenoid valve, the unit would just continue sparking until I would either turn the gas back on or cut power to the furnace. As soon as the pilot would light (albeit for only a second) the sparking would cease. Does anyone know the logic behind that? Does the control box know that the gas has begun feeding so it stops the igniter from sparking or does the DC signal coming back from the igniter/sensor tell the controller that the flame is present and to stop sparking? I guess that would determine whether the igniter/sensor is doing it's job or not.
Thanks. Dick On Sun, 24 Apr 2005 08:26:04 GMT, snipped-for-privacy@comcast.net wrote:

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The control box is looking for a DC signal, somewhere between 0.1 and 5 microamps, depending on the brand of control. Most ignitors have separate leads and electrodes for the ignitor and sensor. The wire with the thick insulation is the spark , the other wire is the flame sensor. Some controls use a single wire/electrode. If the electrode does not have a good ground back to the control box, it will not work well. You may need a competent tech to fix this, as it is, you are playing with fire, no pun intended. With gas, screwing up could be dangerous. You can also go through a lot of parts before you get it fixed. You can also damage new parts if you wire it wrong. If it is more than a bad ground, I suggest you call someone. It's not like the old days when a homeowner could replace his own thermocouple. This high tech stuff requires training to fix right.
Good luck
Stretch
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