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Old 11-26-2008, 06:48 PM   #1
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Lennox Pulse 21 won't fire


I'm working on a Lennox GSR21Q-03-50-1 furnace. Found and replaced bad gas valve. Set pressure (LP) at 9". Won't ignite. Replaced air flapper (original?). Won't fire. Checked spark at module terminal...jumps 3/4" continuous. Plug wire looks ok. Haven't pulled out sparkplug yet. Tried to remove gas flapper and broke wrench! Cut inlet pipe to make sure was getting air, still no fire. Disassembled trap in exhaust to check for obstruction...no fire. Purge fan seems to me to be lazy, only "gentle breeze" at exhaust when it is running. Is this right? Should I pull off the air box to help break loose the gas flapper or have I missed something? This is frustrating!!! Will spark plug socket and imagination remove plug or do I have to have special Lennox tool? Would appreciate any advice short of explosives.

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Old 11-26-2008, 07:26 PM   #2
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Lennox Pulse 21 won't fire


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I'm working on a Lennox GSR21Q-03-50-1 furnace. Found and replaced bad gas valve. Set pressure (LP) at 9". Won't ignite. Replaced air flapper (original?). Won't fire. Checked spark at module terminal...jumps 3/4" continuous. Plug wire looks ok. Haven't pulled out sparkplug yet. Tried to remove gas flapper and broke wrench! Cut inlet pipe to make sure was getting air, still no fire. Disassembled trap in exhaust to check for obstruction...no fire. Purge fan seems to me to be lazy, only "gentle breeze" at exhaust when it is running. Is this right? Should I pull off the air box to help break loose the gas flapper or have I missed something? This is frustrating!!! Will spark plug socket and imagination remove plug or do I have to have special Lennox tool? Would appreciate any advice short of explosives.

Is 9" the right press for lp? You do know that certain of the pulses were safety recalled don't you?

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Old 11-26-2008, 08:33 PM   #3
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Lennox Pulse 21 won't fire


You might want a complete check by a competent tech.
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Old 11-26-2008, 09:58 PM   #4
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Lennox Pulse 21 won't fire


9" wc is what the service manual and a tag on the furnace calls for. I know that you would expect 11", but that's not what it says. As far as "competent tech", I've only been in this business for 29 years and this has me thinking seriously of calling it quits! The recalls were for the earlier models, not the "21's."
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Old 11-26-2008, 10:16 PM   #5
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Lennox Pulse 21 won't fire


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9" wc is what the service manual and a tag on the furnace calls for. I know that you would expect 11", but that's not what it says. As far as "competent tech", I've only been in this business for 29 years and this has me thinking seriously of calling it quits! The recalls were for the earlier models, not the "21's."

Might i suggest Hvac-talk since you are a pro?
Diy sites don't attract too many Lennox guys willing to give up pulse advice.
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Old 11-29-2008, 11:20 AM   #6
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Lennox Pulse 21 won't fire


I am a Lennox tech and got 1 yr on you. Been working on them since day 1 and hate them. The gas flapper is after the gas valve and not in the air box. You need a 5/8 and 3/4 deep socket (I believe) and flex head ratchet, a bottle of tylenol, safety gloves etc to remove the flame sensor and spark plug. The electronic fan timer board is almost obselete and I usually try sell the customer a new Lennox G61V or G71MPP unit as that one is very tricky to repair. I made custom wrenches/shortened some open/box head wrenches especially for those units. Good Luck

More info for you:http://tech.lennoxintl.com/PDFs/9815b.pdf

Last edited by yuri; 11-29-2008 at 11:23 AM. Reason: add more info
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Old 11-29-2008, 02:14 PM   #7
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Lennox Pulse 21 won't fire


LOL Reminds me of an incident.

A Lennox exec literally jumped in my **** (excuse lang) for criticizing the difficulty to access the spark plug and sensor.

I remember when Lennox first unveiled the Pulse at our RSES chapter in Detroit. The place was packed to the rafters. I was still a young business owner then.

The suit from Lennox made the the unit sound maintenance proof.

I didn't agree and told him getting to the spark plug was a bad design.

The Suit from Lennox asked me who I was to question this giant corp. called Lennox.

No surprise. They treat every body like dirt.
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Old 11-29-2008, 03:15 PM   #8
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I have no use for the "suits"/look at the big 3 car execs and their multi-million $$ salaries/results.Currently, Lennox builds a good product, has excellent tech support/training/DaveNet etc. which makes my life easier. Lots of the other brands have very little or no tech support/technical info. Cheers.
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Old 11-29-2008, 09:42 PM   #9
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Lennox Pulse 21 won't fire


I know where the gas flapper is, just broke band wrench trying to unscrew the gas line. I'm going to try a crows foot wrench next. I cn hear the spark so I don't think I'll try removing the plug unless I find nothing wrong with the gas flapper. The "suits" at Lennox out to be condemned to working on these the rest of their days!! To make matters worse, the brilliant installers put it in the attic with the business side facing the narrow side, just enough room for me to lay down beside it.
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Old 11-29-2008, 10:31 PM   #10
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Lennox Pulse 21 won't fire


Hi hoistdoctor

Just wanted to put my two cents in on this one. Its been a while for me, yuri is right the pulse furnace is a pain in the butt to service but still holds the highest efficency rating of its time. They are a very good furnace and I am betting that it has not been properly serviced since installation. That should tell you something of the potential quality. If you are going to tackle this yourself, grab your wallet and be ready. You are going to need a new flame sensor, and ignitor plug. The ignitor plug it uses is similar to a weed eater plug and in a pinch I have even used one. However the gap on the plug is about 80 thousanths of an inch. Not to easy to achieve on a weed eater plug, do yourself a favor and get the proper one. You can buy the service tool for about $25.00 if you go to a Lennox dealer. Don't laugh when you see how simple this tool is, you could easily make one for yourself. But I won't tell you how do to liability reasons. The next thing you need to do is pull the service cap off of the bottom of the flue pipe and clean all of the sludge out of the flue trap and the condensate drain. Last but not least take the six bolts out of the front cover and remove the plate. Take quarter inch nut driver and remove the intake flapper, its a cinch to do. You will need to replace this also when you are getting your other parts. All total you should be ready to spend about $100.00 including the service tool. After you have reasembled the furnace properly listen to how smooth this thing runs. One warning that I have is be carefull removing flame sensor and spark ignitor, there is a very good chance you will cut the back of your knuckles. Use extreme caution and take your time, I have also stripped out flame sensor threads trying to rush removing the sensor. If it feels like it does not want to unscrew easily, keep working it back and forth until it does. Thats about all there is too it, once again don't forget to clean the flue condensate trap, this is a must on these units.

Good luck
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Old 11-30-2008, 10:38 AM   #11
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Lennox Pulse 21 won't fire


If I was going thru all that crap I would be ready to do this.....

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Last edited by hvaclover; 11-30-2008 at 10:40 AM.
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Old 11-30-2008, 10:56 AM   #12
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I would send my junior techs and "talk" them thru it. Can get (2) 24 yr olds for the price of me.
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Old 11-30-2008, 11:16 AM   #13
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Hoist doctor

Let us know how this works out. Believe me when I tell you all the pros I know on the board are rooting for you.

Best of luck.
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Old 11-30-2008, 11:23 AM   #14
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Lennox Pulse 21 won't fire


Hi guys

Not sure if you had the same problems I have had with the junior techs. But most of the time all the money you should have made on a furnace like this one is gone when you have to go back and do it yourself anyway. I actually sent one of mine out when I was still a service manager with written instructions almost as detailed as these, he called me about 10 times and I finally gave up and went and fixed it myself. He unfortunately ended his carrer after this one, he wasn't quite as good as he could talk.

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Old 11-30-2008, 12:55 PM   #15
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I am the senior tech in my company and have several of them "under my wing". Feel sorry for the young guys. We expect them to know how to work on everything from millivolt systems to ECM motors. If they have a good attitude I can get them up to speed, if not they will just be parts changers. The new Lennox G71MPP and other modulating units will put an end to parts changers. If a guy doesn't understand differential pressures/draft and manometers he is toast. Gives me more job security.

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