Any Lennox Pulse experts here....(Starch)

John Starcher_4

...customer called Sunday - they hadn't been up to their "cottage" since September. When they arrived, heat was off and the house was completely frozen.

Furnace is a Lennox Pulse model GSR21-80 (I think, there's another number right below - GSR2104/5-80-1) 80,000 btu input.

First thing I did was check the "air flapper." It was very dirty, so I installed a new one. Still no heat. Next, checked gas pressure downstream of gas valve - just below the drum-shaped "expansion chamber" - no pressure. Verified voltage to the gas valve and incoming gas pressure were ok, then replaced the valve. Now I have the proper manifold gas pressure, but still won't light. Pulled the spark plug, connected a new one and verified spark, reinstalled plug - no results. Just for fun, installed a new combustion air blower assembly, mainly because I was running out of things to check. No luck.

Suspecting maybe a problem with the venting system, I cut both pipes and let them suck and blow right into the furnace room. Still won't light.

So......I have a new gas valve, new air flapper diaphragm, new combustion air blower, new spark plug which I know is getting spark, all controls appear to be working, and no obstruction in my vent system. Oh, I also still have no heat. I'm out of ideas. Any thoughts??

Thanks for any help you can offer.

Starch

Floyd_2

Just a thought....or two...

Lennox had a ton of problems with heat exchangers..replaced a bunch of them... maybe the problem here???
Also I think that I remember the gas press. being only 2" WC on those things.....
There also is a gas flapper in just past that press tap below the expansion chamber..... could be the culprit...

Good Luck!!!!

Floyd


BTW....I hope YOUR drivin to WSII!!!!!!

Mark A. Custis

I thought all the pulses where gone

What board does the thing have? Where did you test the manifold pressure? Did you pull and inspect the gas flapper and orifice? Two thoughts: 1. Low ambiant conditions may not be allowing MGV to open even if you see pressure. 2. Something is living in the gas supply down hill of the MGV.

The only gas flapper assemblies I have had to change was when a four year old played gas station and filled the furnace full of water with a garden hose.

Did you or can you pressure test the heat exchanger? A bad recoup/secondary heat exchange could be leaking so you gas air mix is not under enough static to fire.

I am tired of shovelling snow so I'll get out my book and run the M/# & see if I remember anything more.

Good Luck,

Mark

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John Starcher_4

Floyd and Mark

I attempted to pull the gas flapper out to inspect it, but could not get the @#$% apart. Who in the heck designed these things????????????? I did blow into the pipe connected to the gas flapper, and it was not obstructed, so I didn't see a need to look further at it.

Mark, the control, I believe is a White Rogers, but I can't say for sure, I didn't note the part number on it. I did verify I'm getting spark at the plug, so I figured the control was ok. Did not pressure test the heat exchanger, not sure exactly how to do it....via vent and air intake pipes, maybe?? I was measuring the "manifold" pressure downstream of the gas valve an expansion drum - right at the 90 ell that's just ahead of the gas flapper - there was a 1/8" plug threaded into the back of the 90.

Floyd, you bet I'M doing the driving this time. Murph's gonna meet me at my place, and I'm taking the wheel from here. Can't afford to lose anymore hair, knowhudimean??

Starch

Mark A. Custis

I've got a Lennox

find the leaky heatX kit about 45 mins. due East of you. To get the gas diaphram assembly out, takes the correct socket and a two foot breaker bar. I think something is living in the orfice. The G21 units where not as much on the recall as the G14s. Wife made me clean up when I became self employed, but I know I've got Tech sheets on that unit.

If Murph finds a furnace I may go help him install it. My calender is clear till Thursday unless the phone rings.

Keep me posted

Mark

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John Starcher_4

Mark,

you say low ambient conditions might not allow the gas valve to open? I'm not following you on this, as I can see pressure on my guage, and when I disconnected the vent pipe and ran the unit through a startup cycle, I could smell unburned gas coming out of the pipe.

Starch

John Starcher_4

Mark,

email me, please.

If you have a kit I can use to test the hx, I'd appreciate it. I'll try the socket/breaker bar idea, but what do you use to apply backup wrench to the orifice assy??? Not much room to work in these sunsa-guns!!

Starch

Mark A. Custis

For ignition to occur on a Pulse

The air gas mix needs to be just right and in the right place in the football. If the gas valve is cold it may not open all the way; not enough fuel, no ignition. Even a V-800 won't open if it is too cold (learned that in the middle of the night the hard way).

Found the book

Mark

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Mark A. Custis

JPGs too big

Send me an email off the wall

Mark

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JimmyJam

Pulse problem

John,
Is there a possibility that you could have frozen condensate in furnace? Secondary coil could have blocked passages,on a horizontal G21 there is a drain trap assembly that has a float (ball type) which could be frozen stuck.

If these are not the problem then you need to get an 1& 3/8ths socket to break loose the gas flapper assembly. You can get a 10" pipe wrench wedged in as a backup. The gas flapper should "chatter" as you shake it so as to be metering gas into HX, if it doesn't you have to replace it.

If that is not the case either, leave gas flapper out and then remove (either spark plug or flame sensor, Sorry I can't remember which that lines up oposite of gas tube supplying "football") and run a wire through from inside "football" and out to gas flapper assembly hole to remove any rust or foreign debris that may have accumulated.

I personally do not think that if you have a leaking secondary that it would cause a failure to light unless it was an extreme case. But that is just my opinion.

Good Luck and keep us posted.

ken_6

lennox

did you takeout/apart the float assembly
all condensing appliances have condensate traps
this unit has a floating ball
sometimes they get stuck.
diss assmble clean good

eddie grierson_3

Heat Exchanger

Last HX I had go bad in a pulse, Lennox gave me a new 90+% furnace. Pulses are no longer avalible furnaces or HX according to my salesman. Just thought I would let you know.
Eddie G.

Glenn Harrison

That's just what I was thinking

Frozen secondary and or stuck gas flapper. Also when you replaced the air flapper, did you make sure the spacer washer was still there? (I say this because I accidently left the washer out once).

By the way, the G21's were not part of the heat exchanger recall, just the G14's. That's not to say you might not have a bad HX anyways, especially if it froze. The unit should fire anyways because I have had these where the secondary manifold pipe was falling off and the unit would still run.

Another thing to check is the air intake housing, as I have been finding ones that are melting. You have to have a perfect seal between the HX and the air diaphram.

Last, what color is the ignition module? If it is white or green, plan on replacing it because Lennox has had a lot of problems with them (my Lennox rep even admitted these controls were a piece of junk).

Hope this Helps.

Glenn Harrison, Residential Service Tech

Althoff Industries Inc. Mechanical and Electrical Services

Crystal Lake, Illinois

Althoff Industries website

Glenn Harrison

Come up by me, Mark

We've got thousands of Pulse's around here, most of which my employer put in.

Admitedly they will start disapearing since Lennox no longer makes the HX's for them. We've already replaced a few with bad HX's that the HX was no longer available.

Glenn Harrison, Residential Service Tech

Althoff Industries Inc. Mechanical and Electrical Services

Crystal Lake, Illinois

Althoff Industries website