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Old 05-06-2012, 09:26 PM   #1
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Lennox Merit problem.


Hi folks GREAT site!

I need some advice on an issue with my furnace. When it's been off for a while ( a day or two) it fails to ignite on the first try. Here's what happens:

T stat calls for heat
Blower runs
Ignitor heats (nitride)
gas valve 'clicks' or 'thunks'
ignitor stops glowing without igniting flame
starts cycle 2-4 times before flame lights.

I'm thinking ignitor maybe????

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Old 05-06-2012, 09:42 PM   #2
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Lennox Merit problem.


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Originally Posted by mlijoi View Post
Hi folks GREAT site!

I need some advice on an issue with my furnace. When it's been off for a while ( a day or two) it fails to ignite on the first try. Here's what happens:

T stat calls for heat
Blower runs
Ignitor heats (nitride)
gas valve 'clicks' or 'thunks'
ignitor stops glowing without igniting flame
starts cycle 2-4 times before flame lights.

I'm thinking ignitor maybe????
mmmm could be ...need to prove if gas is flowing when it does not ignite

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Old 05-06-2012, 09:43 PM   #3
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Lennox Merit problem.


Could be. You can check amp draw of the ignitor to make certain it's staying on long enough to light the gas. Those ignitors sometimes get hairline fractures in them which expand as they get hotter, many times cutting the ignitor off just before the gas valve opens.
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Old 05-06-2012, 09:57 PM   #4
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Lennox Merit problem.


WOW! fast replies thanks guys!

I believe the gas valve is opening as there is definately an audible 'clunk' for lack of a better term that comes from the valve after the ignitor is on for about 10-20 seconds.

Is the fact that is could take as much as 4 tries to light the flame lead me to a more specific area?
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Old 05-06-2012, 10:17 PM   #5
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Lennox Merit problem.


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Originally Posted by mlijoi View Post
WOW! fast replies thanks guys!

I believe the gas valve is opening as there is definately an audible 'clunk' for lack of a better term that comes from the valve after the ignitor is on for about 10-20 seconds.

Is the fact that is could take as much as 4 tries to light the flame lead me to a more specific area?
just because you here a clunk it does not mean there is gas flowing..... could be the gas valve the gas regulator the glow coil or burner miss alignment...
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Old 05-06-2012, 10:30 PM   #6
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Lennox Merit problem.


Ok, any advice as where to begin?
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Old 05-06-2012, 10:34 PM   #7
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Lennox Merit problem.


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Ok, any advice as where to begin?
well.... you need a gas pressure gauge to assure there is 3.5 " w.c. to the burner.. you may very well as you are suspecting have a gas valve that is miss behaving..... you need to prove it....
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Old 05-07-2012, 06:40 AM   #8
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What causes the gas valve to open? is it the heat generated by the ignitor or the amp draw of the ignitor?
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Old 05-07-2012, 08:02 AM   #9
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What causes the gas valve to open? is it the heat generated by the ignitor or the amp draw of the ignitor?
niether it is the 24vac that comes from the furnace board....
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Old 05-07-2012, 11:17 AM   #10
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Ok how does the valve know when to open by the CB? Time? I have a new ignitor but is it a stab in the dark if I replace it?
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Old 05-07-2012, 12:41 PM   #11
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Lennox Merit problem.


Gas valve is timed to come on from the control board. The ignitor should be 12-16ohms
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Old 05-08-2012, 02:08 PM   #12
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Ok here's an update. I replaced the ignitor with a universal Honeywell unit this afternoon. Now, furnace won't ignite even after 5 tries and shuts itself down after the 5th attempt. What the heck is going on here. I don't have any HVAC related tools and i'm unsure what to do next. I've taken a video of what happens but I am unable to upload it here.
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Old 05-08-2012, 07:37 PM   #13
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I hope its warm there..... you need a tec to look at it...
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Old 05-08-2012, 09:23 PM   #14
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Did anyone advice you to handle the ignitor by the base only? If you touch the actual part that ignites it's lights out on nitride lighters.
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Old 05-08-2012, 09:30 PM   #15
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Yup I never handled it by anything but the ceramic insulator.

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