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Old 12-03-2011, 09:26 AM   #1
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Another Comfortmaker furnace won't turn on


I also have a Comfortmaker GUH series from the early 90's. It has intermittently locked out leaving the blower running this season. At first it was very intermittent. Now more so. I have a single flash of the indicator and after the prescribed 60 seconds of updraft observe the igniter region getting bright orange. After a no light situation it repeats with a longer igniter period. But still no go.

While checking things out I achieved ignition/flame after jostling the small gas tube that is situated near the bottom of the middle tube. I checked the manuals and nothing indicates where it should be positioned. So the first question is to understand where it should be.

The second question relates to cleaning. I have seen in many places where cleaning is encouraged as a solution. Can anyone describe that in better detail. I am an engineer and quite mechanically inclined but am not knowledgeable about furnaces, per se.

Thanks - also open to any other suggestions.

Oops - I just saw the comment above. Should I make a new thread even though th etopic is the same???

Ron


Last edited by Ron From MI; 12-03-2011 at 09:28 AM.
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Old 12-03-2011, 11:31 AM   #2
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Another Comfortmaker furnace won't turn on


made this its own thread.

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Old 12-03-2011, 11:39 AM   #3
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Another Comfortmaker furnace won't turn on


Look like you need a service tech. Because need to see if gas valve is opening and he will that the right tools for it
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Old 12-03-2011, 12:00 PM   #4
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Another Comfortmaker furnace won't turn on


Quote:
Originally Posted by Tator1076 View Post
Look like you need a service tech. Because need to see if gas valve is opening and he will that the right tools for it
Can I observe any voltage condition for the gas valve to know if it is being requested to turn on? There are 2 pink wires leading to the gas valve (positions 1 & 2) and a jumper between positions 1 and 3.

I agree if it is gas valve related that a service tech is required. That is one area I have avoided playing with in the past.
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Old 12-03-2011, 12:06 PM   #5
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Another Comfortmaker furnace won't turn on


check this video might give you a direction or seach youtube with you problem for a techs suggestions
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Old 12-03-2011, 12:44 PM   #6
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Another Comfortmaker furnace won't turn on


post some pics of it with both doors off and a closeup of the igniter area. there are lots of different versions of that furnace. then we can narrow down the problem.
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Old 12-03-2011, 01:09 PM   #7
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Here are a few pictures. It is a 1992+ Comfortmaker 90+ efficiency 100k BTU GUH100



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Old 12-03-2011, 01:18 PM   #8
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And one more of the igniter. Much of it is covered but here it is.
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Old 12-03-2011, 01:35 PM   #9
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don't have any of those where I am but it looks like that small line is a vent line for the gas valve diaphram. very common years ago. in order to open the diaphram needs to vent gas from underneath itself. try unscrew it completely (temporarily) to see if it will open. if the end of that line is clogged/burnt closed the valve won't open properly. not sure where it should be positioned but it is a VERY small amount of gas that comes out of it so anywhere near the burners w/o it getting melted is OK.
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Old 12-03-2011, 01:48 PM   #10
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Another Comfortmaker furnace won't turn on


OK I'm confused.
The pictures seem to show a gas valve with a skinny aluminum pilot tube going into the exchanger. Is this solely for a crossover feed? because I don't see anything to verify a pilot flame, just the main burners.
I've just seen Yuris post about a diaphram gas valve bleed (which is what it looks like) but I have not seen such a gas valve in anything younger than 78. Maybe "Ron" can show or tell us where this tube terminates?

I was going to say to "Ron from MI" that the next step would be to see if the two pink lines to the gas valve are getting 24V during or after the igniter starts to glow. This would point toward whether the problem in the gas valve or the board.

Last edited by how; 12-03-2011 at 01:57 PM.
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Old 12-03-2011, 01:53 PM   #11
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pic #1 yellow wire goes to the flame sensor I believe. I have seen that yellow wire on other ICPs and if it has a HSI then it has a flame sensor. The round job on the far right burner is one of those old round HSIs that look like a candle. Therefore the flame sensor would be on the farthest left burner where that yellow wire is IMO.
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Old 12-03-2011, 02:48 PM   #12
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I tried checking power to the valve and could not. I wondered what is the appropriate common/ground for it.

I did remove the flame sensor and cleaned it. Yes it has the small yellow wire.

The small line from the valve terminates near the center burner tube. I will try it with it disconnected to verify it is not stopping anything.

Ron
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Old 12-03-2011, 03:00 PM   #13
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Another Comfortmaker furnace won't turn on


you can put your meter on AC volts across those 2 pink wires at the gas valve. should get 24 volts when it energizes. don't worry about the jumper.
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Old 12-03-2011, 03:07 PM   #14
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Thanks I will give that a try
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Old 12-03-2011, 03:18 PM   #15
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Another Comfortmaker furnace won't turn on


A diaphram bleed line should be able to just be unscrewed from the gas valve and blown through. The are usually clamped near a source of flame but if you are able to blow through it you can leave the clamped end in place. If you can't blow through it then the obstruction is usually right at its end near the flame. A paper clip will clear out the debris and if not, removing the last inch of tubing will usually deal with it.

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