Lennox Gas fireplace shuts off


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Old 01-07-11, 02:15 PM
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Lennox Gas fireplace shuts off

Hi I have a Lennox mod#DT3530CNM direct vent gas fireplace. I light the pilot and turn it on no problem. Sometimes it will run all day and shut off and sometimes it runs minutes and shuts off. When it shuts off the pilot and everything goes out. i'm not sure what is the thermocouple either is it the bigger one on the left side or the slimmer one on the right? I don't believe it's an overheating issue. I would appreciate any help, thanks! Tried to load pic but unsuccessful.

 

Last edited by mktgway; 01-07-11 at 02:21 PM. Reason: Load pic
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Old 01-08-11, 09:11 AM
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the thermocouple is the slimmer piece,the thermopile is the larger piece.the thermocouple screws into the valve make sure it is handtight and 1/4 turn...do not overtighten.....below your pilot flame is the pilot head, at the lower portion of the pilot head you should find a small hole,this hole allows oxygen to mix with the pilot gas for a pure burn. dust and such can clog this hole up..take a straw or canned air and clean it out...make sure your logs are off-(no flame)clean the area with air-you do not have to remove the pilot assembly to do this---clean it whether you see dust or not///relite the pilot it should be strong and hitting the thermocouple if the logs t/off after this then you would be looking at buy a new thermo couple and/or a new valve
 
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Old 01-08-11, 09:42 AM
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Thanks so much for the info....I will give it a try. When the pilot is lit it does get the thermocouple red hot when you light the stove. When it does decide to shut off it is like you shut off the switch. I will let you know how it plays out.
 
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Old 01-08-11, 10:24 AM
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Well ....I did everything and so far its still on. Thanks i'll keep you posted.
 
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Old 01-08-11, 10:50 AM
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Upon further review ......it run 50 minutes or so and quit pilot too. What do you think i should try?
 
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Old 01-08-11, 04:50 PM
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your pilot was on for 50 min which means your thermocouple is doing its job at that time....it could still be going bad though...if you have a milivolt tester (sometime on a multimeter) you would disconnect the thermocouple from the gas valve, put your positive lead on the rounded end that ataches to the valve and your black lead on the thermocouple body. the reading should be 13-14 mv with the pilot flame on....this reading must be taken with the pilot flame in operation.....no gas will come out of the hole that the thermocouple was removed from.......note there are 2 different metal wires inside the thermocoupling tube when the flame is applied ithe different metals create a dc current back to the valve, energizing a magnet inside the valve.when you push your control knob in on the pilot position you are pushing a metal plunger into a magnet, the flame is lit so you hold the control knob in for a little while giving the thermocouple time to energize the magnet which holds the plunger allowing pilot gas to go through proving the flame exist and allowing you to continue operation...............you have a thermopile or generator on your logs this looks like a large thermocouple...it has 2 leads connecting to the valve--unscrew these leads and then tighten them snug this will break any corrosion that may exist...........there is not any danger of electrical shock these wires carry millivolts also there is no danger in having the pilot lit while checking the thermocouple being the valve will not be able to be turned on due to it cannot prove a flame without the thermocouple attached......if you cannot take a reading on your thermocouple and none of the other things work i would by a new thermocouple(sometimes the pilot assembly and thermocouple comes together) and try it being it is less costly than the gas valve if that doesnt work then your magnet in the gas valve is weakening and the whole gas valve must be replaced it may be cheaper to buy a new set of logs depending on the age of the existing logs i hope this helps
 

Last edited by barber; 01-08-11 at 05:09 PM.
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Old 01-08-11, 10:40 PM
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Was the fifty minutes with the pilot only being lit, or with the main burner being lit?
 
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Old 01-09-11, 06:22 AM
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I will try that today. Is there any good place to buy parts online? I don't seem to come up with much when I search. Thanks again.
 
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Old 01-09-11, 06:27 AM
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Main and everything was lit, when it shuts off even the pilot goes out.
 
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Old 01-09-11, 07:10 AM
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hvacpartsshop.com has lennox oem parts....i googled the name and model # and this web sight came up....you may be able to find the parts cheaper at a local hvac parts house such as a cc dickson or something
 
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Old 01-09-11, 08:57 AM
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Before buying parts you need to correctly diagnose what the problem is. The main burner and pilot shutting off after fifty minutes of operation suggests that the fireplace may be overheating and shutting off on the limit switch.

That's one thing I'd check.

Frankly, I'd have a good repairman diagnose the problem.
 
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Old 01-09-11, 12:07 PM
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it may be possible that the fresh air intake to the direct vent lennox has been blocked, but i doubt it...if you look at your vent termination you will see 2 pipes, one inside of the other. the center pipe is your exhaust...if the center pipe was blocked then your burner flame would be distorted...it the outer pipe is blocked being this is where fresh intake air comes in then the flame could possbly starve for air---i have never seen this happen.......as far as a limit switch is concerned...well...logs dont have limit switches they only have fan switches if equipped.
 

Last edited by barber; 01-09-11 at 12:50 PM.
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Old 01-09-11, 03:31 PM
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Direct vent gas fireplace aren't gas log sets.

Direct vent fireplaces are pretty sophisticated fireplaces and they have limit switches that on many designs will shut off the main burner and pilot if the fireplace overheats.

And while problems with the venting are common causes of burners being snuffed out, that usually happens within a few minutes of the main burner being turned on.

So I'd say it's unlikely that it's a venting problem, and fairly likely that the fireplace is overheating.

But it takes a careful diagnosis to determine the actual problem, and my guesses aren't good enough to do that.

A good repairman is the right approach here in my opinion.
 
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Old 01-09-11, 05:42 PM
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Yes I believe a good repairman is in order....my problem is finding one. Everyone out here likes to sell but limited service. I do however appreciate all of your input. I did check for any obstructions in the intake and it is fine. Sometimes it will run for a day and you shut it down with the thermostat and other times only minutes.
 
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Old 01-09-11, 06:35 PM
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good idea, as previously mentioned d/v logs are not gas log sets.....i will say that i have been in this buisness for a while and have never seen a limit on a d/v log set. usually from what i have seen the gas valve itself is in a totally seperate chamber from the logs and any tubing enters thru the floor of the box. the only wires on the unit are in the same chamber as your gas valve unless you have a wall switch then of course they lead to the wall switch....i have looked at some manuals and have searched google and i have yet to find anything mentioning a limit switch. the valve is protected by being in the lower chamber of the box and the box is usually surrounded by a large air gab which protects the structure around it...if i am wrong then i would love to be able to find the info proving me wrong but i cant find it..i deffinetly would use this info as a learning tool ...i hoped i helped you to better understand your product
 
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Old 01-09-11, 11:17 PM
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Barber,


Perhaps you are right about limits on direct vent fireplaces. I'm about four years retired from repairing gas fireplaces, and apparently my memory is getting a bit foggy.

As I think about it, the limitations on combustion air supply are so limited on direct vent fireplaces that that may account for the lack of limit switches. Crank up the gas input very much over the rated level and the main burner and pilot get snuffed out.

Still, cut off the air supply circulating around the firebox and I imagine things could get very hot indeed! I'd like to see an explanation from a fireplace engineer on why limit switches don't appear on direct vent fireplaces.

Thanks for pointing out something I apparently hadn't noticed in the past!
 
 

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