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 Repairing and Servicing Lennox Products
 Repairing / Servicing Lennox Gas Furnaces
 Pulse 21
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askthedoc

15 Posts

Posted - 01/15/2011 :  3:34:01 PM  Show Profile  Reply with Quote
My pulse 21 will come on briefly and then shut off. The light blinks one second on and one second off which I think indicates that the low flame sensor is shutting it down. When it runs it sounds sort of rough. So my question is do you think I need to replace the spark plug and see if that fixes it or should I replace the low flame sensor first. Also which spark plug is the proper replacement? Thanks

Matthew

MechAcc

1499 Posts

Posted - 01/15/2011 :  5:33:48 PM  Show Profile  Reply with Quote
Before changing parts it is best to do servicing. It may need just a simple servicing.


Remove rubber cap on bottom of vent drip leg and clear debris. If you have not had the furnace call the Lennox service company and have the heat exchanger pressure tested. Required every four years. Have air flapper replaced. Required every four years. They can also remove and clean flame sensor. Requires special wrench. If you do it with a standard wrench you risk breaking the flame sensor.

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askthedoc

15 Posts

Posted - 01/16/2011 :  3:06:17 PM  Show Profile  Reply with Quote
The drip line is clear. The flapper kit here lists for $300. Is that what you are referring to?

Matthew
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MechAcc

1499 Posts

Posted - 01/16/2011 :  5:50:02 PM  Show Profile  Reply with Quote
$300 would more than cover the servicing, pressure testing and the air flapper in most areas of the country. The heat exchanger really needs to be pressure tested by a Lennox dealer.
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askthedoc

15 Posts

Posted - 01/17/2011 :  10:33:39 AM  Show Profile  Reply with Quote
I hear what you are saying but I am on this forum because I am broke and trying to hope against hope that there is some inexpensive thing that I can do myself to get this thing going. It is over 20 years old and has been a good one. I am just hoping to get a few more years out of it. Hence I was hoping the spark plug and or sensor might be a good place to start. My Lennox guy quit the business and so there is no one really close to me so a service call is going to rough.

Matthew
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MechAcc

1499 Posts

Posted - 01/17/2011 :  12:50:13 PM  Show Profile  Reply with Quote
Sorry to hear about losing your dealer, however if you go to http://www.lennox.com/residential/ in the upper right corner you can plug in your zip code and they will locate a dealer close to you. Sometimes you can locate a hvac contractor though not a Lennox dealer now may have been one in the past and has the knowledge to work on Pulse furnaces.



The air diaphragm will either be the 64L80 or the 64L81. The flame sensor and spark plug requires a special wrench Lennox 20H43 to remove and replace which is not cheap. Cozy has the lowest price that I have found on the web. Use of box end wrenches may or may not get them out and could result in breaking the flame sensor or spark plug. The fact that you have a flame signal error means that a flame is not there. This could be the result of the solenoid gas valve cutting out. Gas orifice dirty and restricting. The purge blower may not be operating on startup. One instance that I ran into some siders took off the intake and vent pipe terminations and swapped the fittings. This resulted in vent gases being pulled down the combustion air pipe and killing the amount of oxygen available for combustion and cycling the furnace off. The gas port across from the spark plug may be agglutinating and disrupting the gas flow pattern. What I am trying to get across is that a good service technician with test equipment can save a lot cost of remove and replace troubleshooting that is done.

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Baltar

192 Posts

Posted - 01/17/2011 :  7:41:12 PM  Show Profile  Reply with Quote
I agree. There could be a dozen or more reasons a Pulse won't start or run properly and throwing parts at it is not the best idea.
If it doesn't hold pressure properly due to a cracked heat exchanger (which needs testing) all the parts changing is for nothing. Plus it is unsafe to use with a cracked heat exchanger.
Cut it twice and it is still too short. :":

Edited by - Baltar on 01/17/2011 7:49:06 PM
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askthedoc

15 Posts

Posted - 01/18/2011 :  10:54:30 AM  Show Profile  Reply with Quote
OK OK I get it. I talked to a friend of my old service guy and found out who took over his service calls so I'm going to go that route. My usual theory is try to fix it myself... if I can't fix it...well I'm no worse off than when I started. Only in this case I cold go through enough money to have had someone (who knows what they are doing) come and fix it right the first time and it might still not work after I've spent all that money. There are just too many variables on this unit to go the trial end error method. Thanks guys for all your input. OBTW the clincher for me was when I saw the $150 price tag on the wrench needed to remove the sensor!!! I don't know if I'll go Lennox next time around.

Matthew
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Baltar

192 Posts

Posted - 01/18/2011 :  5:51:51 PM  Show Profile  Reply with Quote
The Pulse was the only true high efficiency furnace of its time at over 96% efficient on some models and has lasted 30 yrs. Lennox builds high quality units in their high end series and the price of a special wrench for a furnace that saved people thousands of dollars in fuel is not a big deal IMO. All furnaces are fairly similar nowadays (with no special wrenches required) but the Pulse was a breed of its own.

Cut it twice and it is still too short. :":
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askthedoc

15 Posts

Posted - 01/19/2011 :  07:52:11 AM  Show Profile  Reply with Quote
Just out of curiosity how long did the make the pulse and why did they stop making them?

Matthew
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slctech

2085 Posts

Posted - 01/19/2011 :  09:30:54 AM  Show Profile  Reply with Quote
They made the Pulse for about fifteen years give or take a few years. As for dis-continuing production, many outside the Lennox circle who are afraid of them would say they were plagued with heat exchanger issues, bring up a class action suit from the past, and suggest they are impossible to maintain "money pits".
All which is far from the truth.

Truth is that the Pulse technology did make it the most efficient unit at the time. But with all things, technology catches up and the production of similar efficient furnaces which were much cheaper to produce came into play. The Pulse utilizes a very heavy and large heat exchanger system that is expensive to build in both material and labor.
Technology in more efficient heat exchangers, lighter materials, and price of metal steeply rising, lead to a corporate decision to stop production of the Pulse.

I think most of us here have a deeply rooted passion for the Pulse. Personally, I jump to the occasion to service them as a call comes in.



I am not an employee of CozyParts, I generously donate my time. The services here are free, with honest intention to assist, however, this site is not free to maintain. Please make the effort if you need a part or tool to purchase from CozyParts.com. This will ensure this wonderful forum remains for years to come!! As a Lennox Technician I feel basic repairs and maintenance can be performed by the homeowner. But I highly suggest that periodic maintenance should be made by a certified licensed technician. You should contact your local Lennox technician for any repairs or issues that are outside your comfort zone. Property damage, personal injury, and death can occur from improperly repaired or maintained systems. Replacing a part doesn't always resolve the issue that caused the part to fail!
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askthedoc

15 Posts

Posted - 01/19/2011 :  09:38:31 AM  Show Profile  Reply with Quote
Thanks! If we weren't 3000 miles apart I'd have you come right over. lol I'm still enamored with the technology and hope this unit can be repaired.

Matthew
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