Lennox pulse furnace

[Greg K]

I have a 20 year old Lennox pulse 21 furnace. It has a heat pump with propane backup heat. Last winter it quit working one day so I had a friend of mine who repairs furnaces look at it. He poked, prodded, tested stuff and it suddenly worked, no idea why. It worked fine for the last year until Saturday when it quit again, my friends wife is due 10 minutes ago if you know what I mean but he came over and looked again. Same results.
He opened the condensation plug on the bottom of the exhaust and drained what water there was but it all seemed ok. The module is acting like it should, but it will not heat with either the heat pump or the propane backup. The thermostat is calling for heat and the module clicks in and tries to ignite on propane but nothing. Outside temp is 27? F and backup heat is set to kick in at 15?. The intake and exhaust seem clear with no obstructions, I can feel air moving out the exhaust when it is trying to light and I disconnected the intake at the furnace to eliminate any possible issues there.
Does anyone have any ideas? I really can't bother him again since his wife is still very very pregnant.

 

[flying belgian]

CIRCUIT BOARD.

 

[David G]

I would suspect a bad connection.

Does it flash a trouble code?

 

[rrc300 u]

I worked for a Lennox dealer while I was in HVAC school. This was in 1997. What I remember of them things is they had a spark plug and a rubber flapper valve on the qas heat side.
From what you describe the heat pump should be working at this outdoor temp. Lennox did have some proprietary electronics on alot of their stuff. I would not be surprised if the heat pump propane change over was one of those proprietary parts.
You might look at the basic stuff blocked drain or pressure switch tubes being plugged or blocked. Does the vent motor run or does the spark try to light off. If I remember correctly they pop a few times to get the firing set up and burning.
I wish I could be of more help.

 

[Greg K]

Well, the circuit board LED flashes about every second but just a single flash. I just got off the phone with my friend and he said that it was putting out voltage for the gas valve, I can hear it trying to ignite.
Other news is that if the temp differences between the actual temp and the called for temp is too big then it should bypass the heat pump and and go straight to backup heat. So I'm trying that route to see if that is my heat pump issue.

 

[rrc300 u]

Greg whatever you do don't throw parts at that furnace. You will spend some $$$ to do so,they were problems when they were new. You might be better off to find a Lennox dealer to help with this problem. I don't usually give that kind of advice but Lennox is their own animal so to speak

 

[CJinMI]

21 is not new, you are thinkinking 14.
I just popped in for a second, but I'll
be more than happy to help the OP.
I'll check back in the morning.
Sorry I'm short on time tonite,
A Lennox dealer when they came out.

 

[Greg K]

Ok. Here is where I'm at now. The heat pump seems to be working since I turned the thermostat call for heat temp down to within a degree or two of the room temp, then I slowly increased it a degree at a time so it could keep up. As of the last attempt it still would not work on the propane side. I removed the intake pipe (wasn't glued) from the furnace in case it was blocked. I pulled the plug from the condensate at the bottom of the exhaust in case there was any blockage there, however no improvement.
There is 700 gallons of propane so that should be sufficient. When I removed the line inside I had gas pressure that I could stop with putting my finger over the pipe. I poured boiling water over the regulator in case it had some ice in it. I tapped on the electronic gas valve in the furnace in case it was sticking. I'm out of ideas for me. My friend said if he can he'll stop by tomorrow.
Thanks for the input, I remind me of the joke of two guys meeting in mid air. The one going down asks the other one "do you known anything about parachutes?" And the other one replies "no, do you know anything about gas stoves?"

 

[Janicholson]

90% of them failed in the first 10 years. They have defective heat exchangers and can (and have) produced carbon monoxide. They were recalled and if caught before 10 years, fixed. If not identified, they were to be scraped. The heat exchanger develops cracks that cause a improper balance in the combustion gasses. Do not fix it so it works, they are toast. (I owned one and it had those symptoms and a real lenox service man gave me the scoop, and a new 96% efficiency Rheem. Jim

 

[coonie minnie]

As mentioned below, there are issues with the heat exchangers on those. We had a lenox 21, great furnace- little or no maintenance, easy on fuel, etc. However, if the heat exchanger goes, you are done. They don't make new ones. My dealer did offer a sizable discount on a new furnace if my 21 was 20 years old or less. It might be wise to talk to a dealer.

Also: a friend of mine lost his grandfather who tried to install his own gas furnace. I'm told they saw the fireball from I 94. It was an odd funeral. Don't mess around here. You and your family are too important.

 

[Glenn/Mn]

G21 is the latest version, heat exchanger failures more likely with set back thermostats, timed fan delay should be replaced with standard fan control, fan should pre purge eight bolts need to be removed to clean the intake diaphragm, inlet gas pressure is critical for light off, you can also try and ground spark electrode externally to see if module produces when voltage to gas valve is present use a screw driver to see if spark jumps to ground during trial for ignition, I used to teach classes on pulse furnace 30 years retired you can email me if you need to

 

[David G]

I agree with Jim on the safety and longevity of that furnace, but know money can be tight.

I would get it checked by a technician and have the heat exchanger checked, scrap it if any issues.

No reason to put good money into a bad furnace.

 

[andy r]

I have one in a very large farm house. Parents installed it years ago. It has been extremely trouble free. After sitting all summer the fan on the exhaust can get stuck. Mine wouldn't fire up this fall either. Called the Lennox expert in the area. Said it would be a couple days before he could get there. Tore the cover off myself and moved the shaft that sticks through the metal with my index finger. It was truly stuck. Put everything back together and it has worked just fine ever since. Furnace man finally called and I said it was now working. He said the capacitor for that motor looses its potential and very often needs replacing. Said the motor won't start right with a weak one. Said it was about $15.00.

 

[WGM]

The heat exchanger issues were with the G14 model NOT the G21.

 

[CJinMI]

Sent email,let me know if you got it,
if not I'll post a contact info.

 

[Greg K]

Got it. Thanks

 

[Greg K]

My email gets rejected. Maybe call me (four oh two) four oh four-1471