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Old 03-07-2012, 03:23 PM   #16
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Lennox furnace won't stay lit.


seems like a lot of elbows to me....cutting out on press switch.

disconnect the fresh air intake with cover on to see if i runs then.

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Old 03-07-2012, 04:35 PM   #17
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Lennox furnace won't stay lit.


From a fresh start the flame will last for about 30 seconds (just enough time for the blower to kick on), on the subsequent retries the flame will only last about 5 seconds. The flash code is the same:

A. Burners failed to ignite
or
B. Limit open more than 3 minutes
or
C. Lost flame sense more than 5 times in one heating cycle
or
D. Pressure switch opened 5 times in one heating cycle

By "disconnect the fresh air intake..." do you mean from the bottom of the burner box? The air supply line is glued to the fitting for the burner box so I can't disconnect that pipe.
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Old 03-07-2012, 04:53 PM   #18
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Lennox furnace won't stay lit.


I mean the PVC pipe that connects to your burner box.
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Old 03-07-2012, 08:06 PM   #19
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Lennox furnace won't stay lit.


OK so I cut the PVC pipe about 2 inches out from the outside of the furnace (so that I can glue a coupler on it after the test) and it still cuts out at the same time with the burner box cover on it.
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Old 03-09-2012, 09:42 AM   #20
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Lennox furnace won't stay lit.


Any thoughts of what I can try next?
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Old 03-09-2012, 01:13 PM   #21
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Lennox furnace won't stay lit.


now dis connect the exhaust by means of the rubber coupler at the inducer motor.
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Old 03-18-2012, 02:21 PM   #22
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Lennox furnace won't stay lit.


OK I was finally able to get some time to mess around with this again. I took the rubber tub out and let the exhaust go out into the mechanical room and it seems to run just fine. So that tells me that either my inducer motor is going bad or I have a blockage or too many 90 degree turns in my exhaust pipe run.

Am I correct in this assumption?
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Old 03-18-2012, 03:34 PM   #23
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Lennox furnace won't stay lit.


A pro also would manometer the pressure switch hose to see what the "WC measurement is case only the pressure switch is faulty.
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Old 03-18-2012, 03:53 PM   #24
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Lennox furnace won't stay lit.


did you see how many elbows were on the system, how?

yes, check the press switch, but it's not the problem.
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Old 03-18-2012, 03:59 PM   #25
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Lennox furnace won't stay lit.


Quote:
Originally Posted by lucasrj View Post
OK I was finally able to get some time to mess around with this again. I took the rubber tub out and let the exhaust go out into the mechanical room and it seems to run just fine. So that tells me that either my inducer motor is going bad or I have a blockage or too many 90 degree turns in my exhaust pipe run.

Am I correct in this assumption?
so far, yes, with the exception of the inducer being bad.

Just for fun I would use a manometer on the inducer to check the press.

And the press switch too ....but honestly...with you moving in and finding the burner door missing, i am putting my money on too many elbows.
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Old 03-18-2012, 06:56 PM   #26
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Lennox furnace won't stay lit.


Hey HVAC
did you see how many elbows were on the system, how?

Yeah I hear ya and don't disagree but

Today there is a thread with 16 posts which ends with the op saying he fixed his problem by changing his filter.

Would you actually be suprised if the previous owner had a problem with a pressure switch that went away when he opened up the burner door to investigate? It's unlikely that either op had/has access to a manometer.

And

If that system was ever tested & approved, it was with the burner door closed.
Time will tell.
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Old 04-03-2012, 07:56 PM   #27
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Lennox furnace won't stay lit.


That is correct I don't have access to a manometer but am debating on buying one but wondered if you could tell me how much the pressure switches are roughly for my model?

As I see it I either replace the switches (2 x $??)
or
Pay a tech to come out and tell me they are bad ($150 +)
or
Buy a manometer and test them to see if they are bad ($70 +)

Thanks again for all of the help!

I also just noticed that while running it cut out after around 5 + minutes of run time without the burner box cover on. Do you think this points even more so at the pressure switches?

Last edited by lucasrj; 04-03-2012 at 08:10 PM. Reason: saw the issue without the burner box cover on
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Old 04-03-2012, 09:13 PM   #28
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Lennox furnace won't stay lit.


A. Burners failed to ignite
B. Limit open more than 3 minutes
C. Lost flame sense more than 5 times in one heating cycle
D. Pressure switch opened 5 times in one heating cycle

A. Doesn't apply. You have ignition.
B. Temporarily bypassing the entire limit safety circuit will tell you if any of the limits are causing the problem if the furnace runs fine while they are bypassed.
C. Arises from the flame sensor not receiving a good enough signal. This can be because something is pulling the flame away from the flame sensor, a bad board, gas restriction or the flame sensor circuit output is too low.
If the gas is not always enveloping the flame rod, you should probably be able to see that. A meter with a micro amp setting is used to measure the flame sensor circuit to prove if it's good enough.
D. A manometer(in the right hands) will prove if the pressure is fine and the manometer is fauty or if the pressure is too low and the pressure switches are fine.

I also just noticed that while running it cut out after around 5 + minutes of run time without the burner box cover on. Do you think this points even more so at the pressure switches? Not nessesarily!

There are a lot of possible reasons for your furnace problems that a Tech with the proper HVAC tools should be able to identify. Maybe this
is the time to call one.
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Old 05-02-2012, 11:57 PM   #29
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Lennox furnace won't stay lit.


OK so I finally got some time to look into this issue some more. Haven't been too worried about it since summer seems to be here now for us.

But here is what I did. I ran a roto rooter type device through our exhaust pipe to see if maybe there was some sort of blockage (when we moved in there weren't any guards or grates on the supply or exhaust pipes so I was thinking that something could have gotten in there or built a nest etc) and we didn't seem to find anything blocking but when we pulled it back we did find that the end was soaking wet.

So I took a closer look and found that when they originally installed the furnace they covered the drain pipe on the right hand side with sheet metal for the cold air return and also put the sealant over it. So over time it has filled with water.

Also when we had the basement finished 2 summers ago the HVAC guy had to reroute the pipes and ended up leaving the exhaust pipe a little low so the water was backed up in it also. My guess is that there was about 1/2" or maybe more sitting there in the exhaust pipe and thus hindering the exhaust path.

So today I took the black rubber drain hose and cut it and rigged a sort of P trap so that the water could drain but wouldn't let any exhaust fumes out and then I also cut the PVC exhaust pipe and rerouted it so that the pipe just barely angled down enough that the condensation would run into the black drain hose as it should but shouldn't allow it to run down into the exhaust pipe as it had been. This also allowed me to take 3 of the elbows away in the 2" piping that they had.

Well I put the burner box cover on and ran the furnace and it ran for a half hour (that is all that I could bear to run it for since it was hot today) which made me quite happy since it has never run for more than 30 seconds before with the burner box cover on it.

I'll find out for sure this fall/winter I guess.

Thanks again for all of the help/suggestions!

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