Lennox G20Q3E Pilot & Burners Sporadically Won't Light - HVAC - DIY Chatroom Home Improvement Forum

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Old 03-13-2014, 02:14 PM   #1
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Lennox G20Q3E pilot & burners sporadically won't light

Hi guys. A few days ago I noticed my Lennox G20Q3E-75-6 (1997 model) was not putting out hot air.

Upon further inspection, it was evident the pilot light was not lighting. After some fiddling around, I determined that one works-most-of-the-time workaround was to turn the gas valve switch on top of the valve from on to off and back again.

Most of the time this gets the pilot to light right away and eventually the burners light, though sometimes what will then happen is that the pilot stays lit and the burners will cycle on and off a couple of times. That doesn't seem like normal behavior to me, but I don't think that's the primary issue anyway.

At first I suspected the gas valve of malfunctioning, but after reading some forums about my Honeywell valve:

VR8204H 1048

and my pilot igntion control module:

Johnson G776RGD-11

I've concluded it's probably more likely to be the G776 that's causing me grief, and replacing it may be the key. I know I've read more than one thread on this site alone where people report replacing that module with a Lennox 30W33 solved all of their problems.

When things are working well, I see 24 VAC across the PV & MV terminals on the gas valve, and when they're *not* working well (I'm hearing the ticking of the pilot trying to light but it's not), I've seen two effects:

a) Low voltage, maybe 10-12 VAC, which I'm sure is well below what the valve needs to open, so it doesn't and
b) Wildly fluctuating numbers that (on my multimeter) seem to go from 150 down to single digit numbers, but are constantly rapidly changing

So in either of those conditions, the gas doesn't seem to be on.

Also, occasionally when things won't light, I hear a slight humming sound near the gas valve & ignition control module.

So based on what I'm reporting, would you recommend grabbing a new 30W33 and giving that a shot?

Any other simple tests I should try before going that route, just to be sure?

p.s. I also (before doing the multimeter troubleshooting) already compressed air blew out my pilot supply tube and orifices (did not use the small wire cleanout technique yet though, but since the pilot reliably lights and looks pretty strong, I figure that's probably not the issue) and use a dollar bill to attempt to clean up the two rods down at the pilot assembly, which looks something like this:



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Old 03-15-2014, 08:30 AM   #2
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Good chance its the module.


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Old 03-16-2014, 03:05 PM   #3
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Hi Guys:

I have very little experience, but reading these posts and finding a "direct" replacement for the G776RGD-11 box, I found and purchased a Fenwal 35-63J303-117. Although the connectors have moved around, they are well labeled and not a problem.

However, there is a thin rubber hose going to the Johnson unit that is not air, but has a wire in the middle; the same post on the Fenwal unit is quite different and has no contact post in the middle.

What now? Forgot to mention it is a Lennox furnace C23-51

Last edited by citabriabob; 03-16-2014 at 03:06 PM. Reason: clarity
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ignition , lennox g20 , pilot light

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