Lennox Pulse Problems

airflo mech

Here's a little trick for you.take the washer out of air flapper and put some duct tape on one side.reinstall it.we work on them all the time.there's a test kit you can buy to check for cracks.has to hold 4 psi for 10 mins.also check trap.there's cpvc inside trap.hangs 1/2" off the bottom.i found lots of sediment in trap.it can plug cpvc tube.check for co.good luck

Jason_25

Lennox Pulse Problems

pulse won't fire I have gas entering chamber at 3.5 WC I got the special tool to remove spark plug I have spark but no ignition what else to check?

Joe Brix

First....

....verify that your exhaust and intake lines are clear. Next, check the diaphragm media on the burner inlet. That is the most likely suspect. Make sure the spacer washer is in the proper place, between the metal plates. 3.5" sounds high for a pulse - most are rated for 2" WC at the burner inlet.

Starch

Ken D.

Pulse

I agree with John. In addition, the heat exchangers failed on many of them. I have seen ignition problems caused by it. The air flapper is the most likely cause and the washer is very important as John said. Check the "funnel" shaped piece the flapper assy. screws to. Some of these cracked or some of the screw holes stripped out causing the flapper assy. to fit loosely. The gas flapper could cause it, although that is rare. Check the spark plug gap, the ignition cable for deterioration and the spark strength.

Empire_2

Ken D

If I remember correctly, wasn't it the pulse before 1996 that had the HX problem? I can't remember anymore,....:-)
Also check that ridiculous metal basket that was in some models. leaves get caught up in there. When cleaning and or checking the intake flapper as I like to call it, I found it beneficial to use your fingers to clean away the black crap and the oil from your fingers seemed to keep it pliable, longer....

My .02

Mike T.

dana_3

lennox pulse

if you have spark and no ignition, the problem is the air intake flapper gasket. as stated by others, remove the 6-7/16 bolts from the air intake box. then remove the piece of insulation, thats where the air intake cone is. use a 1/4in. nut driver to remove the air flapper assembly.when taking the flapper assembly. pay attention to the way it is put together, including the little washer (spacer) in the middle. the outside faces of the two pieces need to remain facing outside. when apart use a rag to clean off the dirt residue before reassembly. the next obvious question do you know of a lennox dealer(contractor) for the right air flapper media. you will need m# and ser#

JaredM

Pulse

First off, what's the complete model number of what you have. While some of the possible problems have been cited here there are much simpler items to check first. When I have a pulse with no-heat the first things I check are:
-Verify manifold pressure
-Verify purge fan operation
-Verify condensate drain open and trap is clear
-In this weather, verify flue termination is not frozen over

After checking ALL of the above you can start into more complicated items.

-Jared

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

don_156

Lennox

has asked every contractor to test the hx for leaks.

I would ask the customer if they have had it tested.If not
then I would go no further untill it was done.

Why invest the dollars to a lost cause.

I hated to see the pulse furnace come to this...the technology was second to none.

Glenn Harrison_2

Just to refresh

The Pulse recall originally was for any unit made before 1990. After the extremely high failure rate of the recall, and a little more time passing, they found ALL Pulses were prone to early failure of the stainless steel welds on the secondary heat exchanger, along with other places. It was also found that the replacement heat exchangers were/are failing in a short time. That is why they just provide a new furnace with any warranty heat exchanger claim.

don_156

If I may ask

Why the tape?I always found them not to fire at all when the airflapper was dirty or clogged.

Please explain!

Jason_25

Thanks for all the advice I removed and cleaned the air flapper and put back together properly, as for the heat exchanger pressure test kit how do you perform test?

Jason_25

I also checked the purge blower, The vent is clear the pressure switch is closing.

Joe Brix

Is it working now? (no message)

Jason_25

Pulse still not working ,I ordered a new spark plug ,I removed old plug and have spark but may not be hot enough for ignition?

Joe Brix

I would....

...replace the flapper.

Without being there, it's hard to tell what your problem might be. Hmmmm.... Are you getting voltage to the gas valve during the ignition (sparking) phase of the lighting cycle? Is the valve actually opening? What is the manifold pressure when the valve opens?

I'm thinking that if you have spark, the plug is ok. Certainly wouldn't hurt to replace it with a new one, though.

I do not have an answer re: heat exchanger testing on these units, but I would imagine you have to disconnect the vent and intake pipes from the furnace, and then apply a cap to one side, and a air valve to the other.....

Starch

don_185

John corrects.

the test kit comes with all the plugs,prssure guage and a
hand pump to pump it up.

Keep in mind you are working on a pulse.After the first pulse your combustion process is self sustaining.
Your spark and air blower turns off after the first pulse.

Your flappers open and on a negative to add more mixture
and your pressure pulse travel back down and close the flapper and causes the mixture to ignite again.Another pulse.

This happen about 70 time per seconds.That why they need mufflers on them to keep down the dirtbike noise.

Joe Brix

I didn't know....

...that a test kit was available. I'll have to check into getting one. I don't get my hands on very many Pulse furnaces. Does one kit do any model, or are the kits model specific?

Starch

don_156

Hello John

I think they have two differents kits being model specific.

It been about two years since I last work on one.And about
12 years since I last work for a lennox dealer.

How about the complete heat? Have you ever campout with them before?

Joe Brix

No.....

...I have not ever seen a complete heat system. A couple of my larger competitors in this area are Lennox dealers, and we often end up servicing their installs. I have not even heard of anyone in my local area who has a complete heat system. I heard they were a nightmare, so I'm assuming that the local Lennox boys shied away from them.

Starch

Ken D.

Mike T.

I think the recall covered units before "93 or '94, although I could be wrong on the dates. I'll see if I can dig out the service bulletins. Before that, they replaced the whole furnace with a standard condensing furnace. After that they said there was no problem. I did, however find some bad xchangers in the later models. They replaced those also. Those left should have periodic heat exchanger pressure testing.

Ken D.

Pulse

My experience has seen very few bad spark plugs. I would not spend too much time on it. If the gap is good and the plug not worn or broken, check someting else. You can remove the plug and test it off the furnace by turning off the gas and puttiing through the ignition sequence. Be sure to ground the plug. This is best done by an experienced mechanic.