Gas furnace yearly maint+diagnose?


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Old 07-12-12, 07:29 PM
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Gas furnace yearly maint+diagnose?

First a quick intro: i'm a disabled user on a fixed income. I mention disabled because I can get confused and frustrated at what might be obvious to others. Despite that when I was younger my dad taught me how to use tools and stuff, and as long as I understand exactly what i'm doing I can often fix it. (I put a clutch in my car for instance, but it took me months for what should have been a two night job due to severe confusion caused by a medical condition, doing it in the middle of winter was the largest difficulty though) I just explain all that hoping I don't frustrate someone trying to help. My point is when stuff breaks I have to figure out how to fix it myself.

Well the latest thing to break for me was the furnace this spring. It's a natural gas furnace. Not even sure who makes it offhand, no metal plates or brands on it, doesn't say Trane or anything, didn't see an obvious sign on it actually but i'll check again on the followup post, it's only maybe 8-9 years old. I can't afford to hire anyone, if I cant fix it myself I probably wont have heat this winter from the furnace as i'm already on verge of losing my house from medical bills. Last service was maybe 2 years ago, possibly 3 when a control board went out in winter for a still unknown reason, I don't remember who did it/don't have their contact info handy. Whatever yearly service is normally required I honestly dont even know. It was my dads house, I got no manuals, and that 'last service' was probably the ONLY service it's had since new, except for changing out furnace filters. I dont know anything about cleaning blowers, lubricating anything, etc etc. I would like to know if I can figure out what exact model it is where I would go to find out how to do these things myself insofar as possible to try prevent future problems.

But anyway.. there's a problem too. When I turn the thermostat up to start the furnace - nothing now. Was working fine in february, then in march it just.. stopped. I can see no pilot. I've thrown off breakers, reset thermostats and similar - run downstairs to see what it does, and I see no more flame in the little visible porthole that always used to have a flame so i'm guessing that was the pilot. I don't know if it's sparking at all, or just has dirty contacts that I could clean, or what is even safe to inspect or test or do or not. It goes through the rigamarole of turning on the blowers and such for exhaust (not the house blower, thats separate) but never lights off and so it shuts itself back off again. How would I start to narrow down whats needed or maybe it just needs that yearly clean somehow?
 
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Old 07-12-12, 07:40 PM
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Take the cover off the burner compartment of the furnace. Obtain the make and model of the furnace off the rating plate in the burner compartment and post it here.

Obtain the make and model number of the electric gas valve and post that here as well.
 
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Old 07-12-12, 08:41 PM
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I actually don't see a maker listed believe it or not. >_< Nothing I recognize... something says Unitary Products Group on the bottom, and a logo says Gama, neither which sound like furnace brands I know of offhand.

However Model # lists as g9t08012upb13c which a google search shows either Coleman or Luxaire. (I think a metal logo had fallen off the furnace during the past service and got misplaced or something)

Input BTU 80,000 output BTU 74,000

I'm guessing the gas flow valve was the piece with the following information - Gemini 36G24Y, Type 206. Is more information needed?

I'm going to try and borrow a small digital camera from someone as soon as I can if that will help but I don't have one handy just yet. (and dont know if I can post pictures here anyways or how that works)
 
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Old 07-13-12, 05:39 PM
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As I understand your post, when the thermostat is turned up the inducer motor which circulates combustion gasses through the furnace turn on and comes up to speed. Is that correct?


Your furnace has what's called a hot surface ignitor, which glows white hot to light the gas. After the inducer motor comes up to speed, the HSI should heat up and be easily visible, like a light bulb being turned on near the furnace burners.

I presume that is NOT happening, is that correct?


The HSI can burn out, but if it does the gas would be turned on for 3-5 seconds to see if the gas lights off the HSI. Does that happen?

Usually if it does you will hear the electric gas valve turn on and perhaps smell gas being released by the burners.
 
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Old 07-14-12, 09:23 PM
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Unless I misunderstand how things are working (possible but I think I mostly know what is what) yes. An internal blower to the furnace itself (separate from the whole house circulation squirrel cage blower) turns on when I raise the thermostat. Previously (i'd watched it during past problems where it was short cycling) i'd hear the tick tick tick of sparks (I forget how often, I didn't check it just now) trying to trigger off the pilot. I remember hearing solenoids trip, then the spark tick, and it would normally fire off the pilot then which would visibly glow, and then start up the main burner which was visible as well. I no longer hear or see that, the gas solenoids sound like they turn on but there's no spark tick, therefore nothing lights off. The gas turns back off, blower runs for awhile, then it tries again maybe 3 times before giving up. (guess from memory but I tried it two dozen times back then) I've seen it light off in the past and it's definately not lighting off anymore. I don't remember smelling gas though. I'd like to know if this is something that was supposed to be cleaned, like if it's something that just gets dirty after awhile, and how to test it safely to see whether spark is not getting to a good igniter, or if the igniter just pooped out, or what exactly. All I know is it worked as of february or so, then just went 100% dead overnight. No slow degradation that I was aware of. PS why wont this let me hit return to break up a solid wall of text? I keep editing and it wont save formatting. :P
 

Last edited by brokendown; 07-14-12 at 09:29 PM. Reason: keeps pooping out a solid block of text
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Old 07-14-12, 11:14 PM
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Here's the manual for your furnace: http://m.master.ca/documents/G9T-UPI...ation-0304.pdf
 

Last edited by user 10; 07-14-12 at 11:34 PM.
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Old 07-15-12, 12:51 PM
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Thanks! Though that's only for installation, I didn't see maintenance/repair/diagnostic information in there. But at least it helps me narrow down which part is doing what - the drawings I was looking at at least do look like the interior of my furnace so far.
 
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Old 07-16-12, 09:40 AM
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Since the gas turn on for 3-5 seconds but the hot surface ignitor doesn't get hot, more than likely the hot surface ignitor is burned out.

Look for the hot surface ignitor near the front of the burners. Remove and inspect it ---usually a matter of removing one or two screws.

A bad ignitor usually has a visible crack, often surrounded by a whitish powder.

If that's the case, you need to buy and install a replacement ignitor.
 
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Old 07-16-12, 11:24 AM
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brokendown mentioned hearing a spark igniter - is it possible that there's an earlier revision of that furnace with spark ignition?
 
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Old 07-16-12, 08:24 PM
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Possible, but a HSI is far more likely.
 
 

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