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Old 11-12-2011, 02:13 AM   #1
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Lennox Superior Fireplace Problem


Hello everyone. I need a little help. I'm having problems with a Lennox Superior gas fireplace that was installed in our home about 4 1/2 years ago.

The fireplace is controlled by a standard wall switch. The pilot light is fine and remains lit. At first, I was having problems starting the fireplace when I turned on the wall switch. Sometimes I would need to flip the switch on and off several times before the fireplace would ignite. The problem has become slowly worse and today the fireplace mysteriously cut off after it had been operating for about 20 minutes or so.

I've read that sometime the wall switch can build up an electrical resistance and may need to be changed. However, I do hear a faint click in the fireplace when I turn on the wall switch. I've also read that I may need to sand soot off of the thermocouple, but I have no idea what that looks like or where it's located. Any help is greatly appreciated.

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Old 11-12-2011, 07:25 AM   #2
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Lennox Superior Fireplace Problem


Try going to:
http://www.lennoxhearthproducts.com/...ireplaces/gas/
download the manual for your fireplace insert; it has troubleshooting advice.
I'm 99.9% sure it isn't your wall switch.

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Old 11-12-2011, 08:33 AM   #3
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Lennox Superior Fireplace Problem


I would replace the wall switch. they use a millivolt system (3/4 of a volt or less) and those light switches cost $1-2 and do wear out or get corroded. make sure you have bare copper and tighten the wires nice and snug on the new switch. voltage is so low it cannot hurt you so you don't have to turn anything off. just don't touch them to anything metal or the gas valve will shut down.
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Old 11-12-2011, 09:22 AM   #4
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Lennox Superior Fireplace Problem


Since the fireplace uses a millivolt system should I purchase a special wall switch or just get a standard one?
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Old 11-12-2011, 09:44 AM   #5
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Lennox Superior Fireplace Problem


standard one. get a new one and not some used one or sitting in a damp basement or garage one. takes VERY little resistance to stop a millivolt system.
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Old 11-12-2011, 10:01 AM   #6
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Lennox Superior Fireplace Problem


Okay, thanks!
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Old 11-12-2011, 03:43 PM   #7
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Lennox Superior Fireplace Problem


I find that often the pilot flame is partially restricted enough to not envelope the thermopile adequately. This reduces the dcv so that minor resistance stops the fireplace from working. You can try tapping the metal beside the pilot assembly with a large screwdriver while the pilot is burning and the vibration plus the pilot gas pressure will often dislodge any obstructing debris. You will notice the pilot flame becoming larger if you are successful. If the fireplace then fires up, the wall switch will not need to be changed.

Of course perhaps opening up the fireplace to access the thermo pile is more trouble than a wall switch change but should be kept in mind if the wall switch change doesn't correct the problem.

Last edited by how; 11-12-2011 at 03:45 PM.
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Old 11-12-2011, 03:48 PM   #8
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Lennox Superior Fireplace Problem


Good suggestion. What does a thermopile look like?
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Old 11-12-2011, 03:58 PM   #9
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Lennox Superior Fireplace Problem


If you look at your pilot flame, the powerpile will be bathed by the pilot flame and be about the same width as a cigarette. When tapping the metal around the pilot assembly, don't accidently hit the little pilot igniter or you may damage it.
Bobs suggestion for downloading your manual is worthwhile for showing how to access the pilot(if you need to) as well as showing what the parts are what.

Last edited by how; 11-12-2011 at 04:01 PM.
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Old 11-12-2011, 04:05 PM   #10
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Lennox Superior Fireplace Problem


What does the thermopile do and how does that differ from the thermocouple?
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Old 11-12-2011, 04:17 PM   #11
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Lennox Superior Fireplace Problem


A thermocouple produces a fraction of the power a thermopile does. A thermopile is a collection of thermocouples that produces enough voltage from the pilot flame to run your gas valve, safety limit controls and thermostat/on-off switch.
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Old 11-08-2012, 05:41 PM   #12
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Lennox Superior Fireplace Problem


I started up my Lennox gas fireplace today (Model LMDV-4035CNM) and I'm having the same problem as last year. According to the troubleshooting guide in the owner's manual I'm supposed to do the following:

Check thermopile with millivolt meter. Take reading
at thermopile terminals of gas valve. Should read
325 millivolts minimum with optional wall switch
“OFF.” Replace faulty thermopile if reading is below
specified minimum.

This particular gas fireplace has a SIT Millivolt Natural Gas Valve. There are three terminals labeled TPTH, TP, and TH. Using a voltmeter, where do I place the leads to measure the voltage?
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Old 11-08-2012, 06:39 PM   #13
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Okay, I just tested the TPTH and the TP terminals and I'm getting 460mv with the wall SWITCH OFF and 200mv with the wall switch on.

The weird thing is if I hold the voltmeter leads on the two terminals, the voltage with the SWITCH OFF will slowly rise from 460mv to 492mv. If I hold the voltmeter leads on the terminals with the SWITCH ON the voltage will drop from 200mv to 186mv. I waited about 10 minutes and the SWITCH ON voltage stabilized around 183mv. So far the fireplace remains lit. I'll keep an eye on it and see what happens.

What does this indicate?
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Old 10-12-2013, 10:29 PM   #14
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Still having problems. Bumping this old thread for help.
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Old 10-13-2013, 05:17 AM   #15
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Lennox Superior Fireplace Problem


Replace that switch.

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