Lennox furnace help


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Old 02-21-18, 01:10 PM
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Lennox furnace help

I have a lennox furnace model number GH19Q3/4-100
I am having trouble with burners going off mid cycle and restarting.
I tried to clean the flame rod, but want to know how to get to it. It looks buried in burner.
Its on a horizantal furnace.
any help would be appreciated.
 
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Old 02-21-18, 05:21 PM
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Not going to be an easy fix. There isn't a flame sensor rod per se. It's a combination ignition spark system with flame sensing.

It looks like the gas manifold and valve are removed along with the pilot tube and pilot assembly for servicing. You could have a dirty ignition rod or a dirty pilot orifice. I'd recommend professional service on this unit. You could try your gas provider. They usually have good technicians.

The link is for your manual. It's very informative.... LennoxGH19.pdf
 
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Old 02-21-18, 05:30 PM
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I found this manual already thx, But does the rod stall act the same as a regular flame rod?
Looks like you have to take the whole burner aseembly out to change is that how?
 
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Old 02-21-18, 06:13 PM
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Yes and yes.
My point is it might not be a dirty rod. A dirty pilot orifice is a common problem.
 
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Old 02-21-18, 07:09 PM
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ok thx for help . not sure when Ill do anything its working for most part now. So might wait till slightly warmer weather.
 
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Old 02-22-18, 10:23 AM
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Any chance of being my control board? Or more likely to be dirty pilot orfice?
It always seems to light back up, burner will just go out mid cycle
 
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Old 02-22-18, 01:20 PM
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i wonder if the limit switch is shutting off the burners on overheat, then allowing them to restart when the heat exchanger cools down?
Is the filter clean, and have you tried putting the blower on a higher speed to see if that helps alleviate the issue?
 
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Old 02-22-18, 04:29 PM
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The filter was dirty, I changed it but still no difference. I have not changed the fan speed.
Ill have to read how. It was working fine for couple years.
 
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Old 02-22-18, 04:42 PM
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With that furnace..... the pilot light is monitored by the flame sense circuit. So if there is a pilot issue.... the circuit could fault.

The only way to determine if it's a safety switch or the ignition system itself is to monitor the 24vac on terminal 5 and 6 of the ignition module. If the voltage and the burner shut off..... it's a safety or limit switch. If the voltage is present and the burner stops.... it's an ignition issue.
 
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Old 02-22-18, 05:53 PM
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thx prob be next week before I test anything unless it goes out completely
 
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Old 02-22-18, 06:17 PM
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Unfortunately.... since it's an older unit... it's before they came out with fault LED's on the control boards... so it requires more legwork to diagnose.
 
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Old 10-14-18, 10:06 AM
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still have this same issue with the furnace starting this year. It does appear once limit switch is cooled down the burners come back on. is it possible to change the fan speed.
if so how it has 3 wires to fan red white and blue. 4 connectors to fan.

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Old 10-14-18, 10:24 AM
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It does appear once limit switch is cooled down the burners come back on.

Sounds like an airflow issue to me too, but I can't offer much assistance on how to increase the fan speed other than to check the label inside the blower compartment. I do know that some filters offer more resistance to airflow than others and your issue can sometimes be solved by changing to a less efficient filter. I had a similar issue years ago and when replacing the furnace found that it was grossly oversized for the house and ductwork.
 
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Old 10-14-18, 10:38 AM
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Your picture is of the motor. Any changes would be made at the opposite end of those wires.

Too many closed down registers can cause an airflow issue too.
 
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Old 10-14-18, 02:33 PM
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ok does seem like a flow issue but nothing has changed. I did look at it some today. I dont know if anything or not, but one of the return pipes came apart. So i put it back together. Not sure if not drawing air from living space would cause this or not?

Pete, is the opposite end where I change the wires on the control module?
 
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Old 10-14-18, 03:01 PM
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Yes.........................that is correct.
 
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Old 10-14-18, 05:31 PM
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reason I was thinking needed to be changed on motor was thats what it seems like the manual states?


know which ones need changed?
 
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Old 10-16-18, 10:22 AM
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Do u know what wires I move to where ?
 
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Old 10-16-18, 04:26 PM
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Has anyone covered up any of your returns. You're only going to get as much air out as you have returning. If your returns are covered it's like putting your finger over a straw full of water.

Your furnace will short cycle on high limit bt no air will be delivered even if blower is on.

Just a thought. Also you might want to check your dampers if you have any on your supply pipes.
 
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Old 10-16-18, 04:52 PM
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I need to see a picture of the board where the wiring connects to advise.

Good info from spott.
 
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Old 10-16-18, 05:30 PM
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I have checked the return vents nothing blocked.

I will try to get pics wednesday of the board
 
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Old 10-16-18, 07:45 PM
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Sounds as though it's been diagnosed as an over-heated furnace with no mention of checking the temperature rise. Even if it is overheating you would want a TR for a base-line to confirm your attempts at cooling it down. From the wires I see at your motor the speed choices will be very limited.
I believe post# 19's description of a static pressure issue could be on the right track.
A carbon monoxide test would also be in order if it's been repeatedly going off on high limit.
 
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Old 10-17-18, 03:20 PM
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would open return line in crawlspace possibly relate to overtemp from non air flow?
I found a couple return pipes apart. ?

also seems to work fine when temps outside are around 30-40+ degrees.
when gets really cold is when it acts up
 
 

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