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Discussion Starter · #1 ·
I have a two zone heating system (Lennox elite series) furnace. Zone 1 works fine. Zone 2 does not. Thermostat call for heat. Burners ignite, but doesn't stay lit. After three minutes of cycling on/off the system goes into the safety watch guard mode(alternating slow flash). I checked the dampers they are working fine. Once and a while zone 2 will fire up and work fine??? What could be the problem considering zone 1 works fine? Bad thermostat?
 

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You are contradicting yourself. If the burners don't stay lit it is a furnace problem. Post the model and serial # as I am a Lennox tech.

There should be a error code when it is trying to stay lit. Have you cleaned the flame sensor or had it serviced?
 

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Discussion Starter · #3 ·
Thank you for taking the time to respond. Model #G60UH-36A-07-05. Serial #5904F30800.

Flame sensor was just replaced last winter. I probaby wasn't clear on my first post . My upstairs zone has its own thermostat and works perfect. The furnace kicks on, stays on and heats the upstairs. The downstairs zone is the problematic one. It has the issue described in my last post.

Since the upstairs is working i didnt think it was a furnace issue so I was leaning towards a wiring/thermostat issue. I checked both the control board and themostat for any loose wiring and found nothing. I also just changed the filter.
 

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It cannot work fine in 1 zone and not the other. If it is going into Watchguard then you either have a furnace problem or not. Is that happening or not or why did you post it?
 

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Discussion Starter · #5 ·
why do you say it can't work fine it one zone and not the other? I am watching it happen. couldn't it be a thermostat issue?
 

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watchguard means the flame failed or the limit stayed open longer than 3 minutes or the pressure switch opened 5 times in a cycle or it lost flame 5 times in a cycle.

Is it going into watchguard or not? If you cannot answer that I cannot help you.

The zoning panel just turns the furnace on. Has nothing to do with it working properly or not. The 2 tstats tell the panel to tell the furnace to start.

It does not go into watchguard w/o giving some error codes while those scenarios are happening.
 

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Discussion Starter · #7 · (Edited)
Thank you for the reply. The system definitely is going into watch guard mode, but only when I turn on tstat #1. I then have to kill power to system to reset. When I turn on heat from tstat # 2, the furnace does not go into safeguard mode at all.
 

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I know that furnace VERY well. The flame sensor needs to be cleaned once a year with clean steel wool or #800 emory paper AND the face of the burner it sits in front of must be cleaned to remove the rust on it and the metal ring inside. Lots of techs do not know that. It is part of the flame signal process.

Google : DC flame rectification for more info. Not easy to get at the burner as the metal plate over them needs to be removed etc.

Not sure what else can be your problem. If the zoning panel is not sending a proper 24 volts to start the furnace then it may aggravate the board and cause it to do that. I see very few of those panels so it is just a guess. Time to call a Pro.
 

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It would show a high limit code before going into watchguard. He should easily see that.
 
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