Lennox P21

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  #1  
Old 10-03-08, 06:34 AM
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Lennox P21

I just moved into a home and thought my furnace was working... was I wrong. The furnace is a Lennox P21. It was purchased in 92... I can tell by the serial number.

Problem: The furnace only starts when it wants to. For example, if I turn the power off and back on, it works sometimes. Most of the time it does not. When it works, it only works for like 15 minutes and shuts off. When it shuts off a green blinking light occurs for 2.5 seconds on the igniter control.

What I have done thus:
1. Intiated furnace by thermostat
2. Restarted furnace with switch for greater then 10 secs
3. Restarted furnace for over 1 hour
4. Replaced diaphragm and gasket
5. Cleaned flame sensor connections

The guy at the only lennox shop near us is extremely busy and does not have time to come out to my place today. He recommended replacing the igniter control, but not sure that is the problem if I am getting a blinking light (and it is expensive). What are you thoughts?

It is cold up here in the upper peninsula of MI! Wife and kids are not happy. Please help!
 
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  #2  
Old 10-03-08, 07:06 AM
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Did you mean G21? What is the full model #?

if so, this is a Lennox Pulse furnace.

Check to be sure the pipes outside are clear, and not blocked off.

When you call for heat, do you hear a small inducer fan running to purge out the heat exchanger?

After about 30 sec, should be a click, the furnace should start to "rumble" (pulsing), then the small inducer fan stops.

Looking at the furnace on the side is the exhaust pipe. There is a tail pipe that drops down about a foot or so. Is there a sign that has been cut? If not, get a rubber hose coupling, and then cut the pipe, I bet it needs to be cleaned out.

Also, Is there any sticker/tag on the furnace saying the heat exchanger been pressure checked?
 
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Old 10-03-08, 07:32 AM
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re: Lennox P21

Thanks Jay -

Did you mean G21? What is the full model #?
- It is a Pulse 21 (G21Q). Sorry about the misunderstanding.

Check to be sure the pipes outside are clear, and not blocked off.
- The pipes do not appear to be blocked off.


When you call for heat, do you hear a small inducer fan running to purge out the heat exchanger?
- Yes

Looking at the furnace on the side is the exhaust pipe. There is a tail pipe that drops down about a foot or so. Is there a sign that has been cut? If not, get a rubber hose coupling, and then cut the pipe, I bet it needs to be cleaned out.
- This maybe the issue. I have a pump next to the exhaust pipe that was extremely full. I have emptied it and the furnace seems to be functioning properly (about 20 minutes). The longest I have had it work is around 30 minutes. We should find out shortly if this fixed the problem. The exhaust pipe does not appear to have been cut before, but I am guessing that is why they placed the pump tube to the exhaust pipe. Have you ever seen this before? Is this common? I will try to empty the exhaust pipe if empting the pump does not work.

Jay - thank you very much for your answers thus far.
 
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Old 10-03-08, 07:47 AM
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Originally Posted by jamiechipper View Post
This maybe the issue. I have a pump next to the exhaust pipe that was extremely full. I have emptied it and the furnace seems to be functioning properly (about 20 minutes).
Some times there is a interlock switch on the pump. If the pump did not work, it will shut down the furnace. Has the pump been running to remove the water out of it?

The exhaust pipe does not appear to have been cut before, but I am guessing that is why they placed the pump tube to the exhaust pipe. Have you ever seen this before? Is this common?
The drain hose coming off the exhaust pipe is a common thing. There's water inside that pipe that needs to drain away. SOunds like you don't have a floor drain near by so a pump is used to pump the water away to a sink or something.

The water has to flow free in this hose/pipe, and if it don't it will shut down the furnace.

If the pump does run and chances are there are "junk" in that tail pipe that is blocking the water drainage.

So like I said when you cut that pipe, you will have to put it back on with a rubber pipe coupling.
 
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Old 10-03-08, 08:04 AM
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re: Lenox 21

Some times there is a interlock switch on the pump. If the pump did not work, it will shut down the furnace. Has the pump been running to remove the water out of it?
- No - that is why I think this maybe the problem.

SOunds like you don't have a floor drain near by so a pump is used to pump the water away to a sink or something.
- You are exactly right. Thanks for the clarification.

Thanks again. Looks as though I am headed down the right track with this one thanks to you. You saved me atleast $250. The people wanted me to install the ignitor control. The furnace is still running!
 
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Old 10-03-08, 08:47 AM
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Glad to help you out.

The Lennox Pulse are no longer made and lot of service guys has not had much experince with it, and some time they make this simple furnace "complex" where it's really is not.

If you have not see any sticker around the furnace of having a Lennox Dealer do a pressure testing of the heat exchanger, I would suggest you get one done.

Sounds like you got the intake and exhaust flapper replaced, so you should be good, since that is something should also be done.

These heat exchanger are been known to crack, and would suggest to get a CO Detector in your home.
 
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Old 10-03-08, 09:58 AM
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re: Lennox 21 - hopefully last questions

Couple more questions Jay -
1. What exactly does the pressure test of the heat exchanger do?
2. How much water should be coming out of the heat exchanger. I am getting about 1/2 gallon every couple of hours now and need to change out the water because the pump seems to be broken. Is this going to occur often? The reason why I ask is because we are in a pretty remote area and there are not too many hardware stores around. Should I get the pump replaced now or can it wait a couple of days? Will the condensation cease at some point?

Thanks!
 
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Old 10-03-08, 01:30 PM
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Originally Posted by jamiechipper View Post
1. What exactly does the pressure test of the heat exchanger do?
The pump air into the heat exchanger and put it under pressure, then they let it sit for abit and watch the pressure gauge.. if the pressure drops, then there's a leak/crack in the heat exchanger. If no change in pressure, then you are good. I would have to checked every other year.

2. How much water should be coming out of the heat exchanger. I am getting about 1/2 gallon every couple of hours now and need to change out the water because the pump seems to be broken. Is this going to occur often?
Yes, the more the furnace runs, the more water you are going to get.

You made sure the pump is plugged in, and do have power at the outlet?

The reason why I ask is because we are in a pretty remote area and there are not too many hardware stores around. Should I get the pump replaced now or can it wait a couple of days?
I would replace it before winter sets in. So plan a trip some time to get a new pump.. You can find them at Home Depot, or else where.


Will the condensation cease at some point?
Nope, it's going to have more as winter comes.. The water is coming from the combustion, and when it goes over the secondary heat exchanger, it's extracting as much heat out of the exhaust gas before it sends it outside in the PVC pipe. That's how a 90% furnace works. (90% of the heat from the gas goes into the home, and rest goes out to waste, and able to use PVC exhaust)

Do you have A/C? If you did, where did the water go for that?
 
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