Lennox 90UGF condensation issue


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Old 02-04-11, 10:51 AM
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Lennox 90UGF condensation issue

Hi all,

My Lennox 90UGF only starts intermittently during very cold winter days.

From the sounds of it when it doesn't start, the combustion air blower is sloshing through water built up in the condensation unit. Sometimes, if I cycle the furnace on and off enough, I can get the ignition cycle to catch (sometimes only lighting burners for a few seconds other times it runs for 30 minutes), but mostly the combustion air blower just keeps spinning and spinning.

I have checked that black plastic (1/2"??) flexible pipe from the air blower down to the condensation trap is free of debris. The vertical part of the condensate trap line (goes left, plugged right) to floor drain is also clear (easily checked as the A/C condensation line joins and drains down via that part).

BUT ... when I take the black flexible pipe off the nipple at the condensate trap and drain the water from it and then re-attach it, the furnace always starts fine. The combustion air blower now has enough umph to get the ignition cycle all started. That said, after hours of running and when the furnace stops, it doesn't take long for the water in that pipe to stop the furnace from re-firing the next time.

I don't want to have to take the combustion air blower off (or do I?) and vacuum out the condensation pan/unit, so can I simply get a longer 1/2" flexible pipe, and hook it up directly to the top of the combustion blower motor down to a drain bypassing the condensation trap so that this water drains constantly?

Or should I first check that the 14-18" horizontal (left) run of 1" (?) pipe from the condensate trap to the vertical line down to the drain is clear of debris? I guess I'd do that by removing the plug on the right side and running a thin plumber's snake left?

Thoughts?

Thanks.

P.S. There is no squealing etc when the combustion air blower is running. Whe the furnace does catch, it's smooth and quiet. There are also no leaks, drips or signs of junk or corrosion at all on the panel under the combustion air blower and condensation unit.
 

Last edited by DaveyJJ; 02-04-11 at 11:50 AM.
  #2  
Old 02-04-11, 11:19 AM
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The trap is essential to the operation of the furnace.

The inducer motor is designed to keep that portion of the furnace under negative pressure to cause combustion air to flow through the furnace. Eliminate the trap and that negative pressure will be lost due to air flowing into the furnace through the pipe.

A trap plugged up with mold isn't unusual. Your methods so far apparently haven't cleaned it adequately.

You may need to remove the trap in order to clean it thoroughly, or even replace it.

You may want to devise a means to be able to remove and clean the trap easily in the future when you reinstall it.
 
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Old 02-04-11, 11:47 AM
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Hi, sorry, I think I might not have explained well enough.

I wasn't suggesting I remove the 2" (?) trap cover in the bottom of that T under the condenser unit (on the right) and drain water from there and leave it uncapped, rather that I simply run the much smaller diameter flexible black water (shown as solid red) pipe that currently runs from the second part of the top of the combustion air blower down into the T that is the condensation trap fitting (1), and instead just drain that small pipe separately (2) to the floor drain.

I'd simply use a 1/2" cap to close the now open nipple (1) on the condensation trap.

Once that smaller diameter pipe starts gets filled with water, that's when the furnace refuses to restart. (That's why I was also suggesting trying to clean out the pipe run from the T condenser trap that runs out left across the other vertical drain run.)

Condensed water isn't draining from somewhere effectively. Could the flue pipe be blocked, and if so, how do I access it? The back of my furnace is almost inaccessible.

 

Last edited by DaveyJJ; 02-04-11 at 12:04 PM.
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Old 02-04-11, 12:34 PM
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Check the small hose from the inducer (combustion) blower to the pressure switch. If it is long enough to have a "sag", it can trap condensate and prevent the pressure switch from operating. If this is the case, shorten or tie up that hose so it drains back into the blower housing.
 
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Old 02-04-11, 12:40 PM
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Originally Posted by goldstar View Post
Check the small hose from the inducer (combustion) blower to the pressure switch. If it is long enough to have a "sag", it can trap condensate and prevent the pressure switch from operating. If this is the case, shorten or tie up that hose so it drains back into the blower housing.
I'll check that as soon as I can get home after work and let you know, thanks.

Also, if I did want to remove the entire combustion blower motor assembly, can I remove only the centre portion (four screws) or do I have to remove the whole (bigger) unit? And is there any risk of a carbon monoxide leak when working on (removing and putting back in) the combustion blower motor?
 
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Old 02-04-11, 03:53 PM
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Originally Posted by goldstar View Post
Check the small hose from the inducer (combustion) blower to the pressure switch. If it is long enough to have a "sag", it can trap condensate and prevent the pressure switch from operating. If this is the case, shorten or tie up that hose so it drains back into the blower housing.
Nope, no sag on that. A nice gentle 6" or so curve, tightly sealed, no moisture inside it.
 
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Old 02-15-11, 12:04 PM
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Hi DaveyJJ,

I had similar problem and when I drained and cleaned the black pipe the furnace started to work as expected, but I'm wondering when it will do it again. Did you resolve your problem?

Thanks!
 
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Old 02-15-11, 12:07 PM
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Oddly enough, mostly, yes. goldstar's note to check the small hose prompted me to have a close look at it by pulling it off. I managed to blow out one or two drops of condensation from that hose and the furnace has been largely fine since.
 
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Old 02-15-11, 12:26 PM
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Thanks! I'll check mine tonight!
 
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Old 02-15-11, 02:06 PM
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No problem. I think that the combustion air blower is still sloshing through water at times when trying to get going after long overnight off periods, but it seems that after I cleaned out the rubber boot and drained the larger (solid red) highlighted hose, it's able to clear itself out when starting and the furnace is running much better.
 
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Old 02-15-11, 04:46 PM
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I checked the small hose that goes to the pressure switch. It was clean, but the black rubber hose (the one you coloured in red) had some water in it, but wasn't clogged, which I guess is the normal situation and the things get worse only when there is something that clogs the black hose.

Hopefully the furnace will work OK at least for the rest of the winter!
 
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Old 09-11-11, 08:07 AM
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just resolved similar issue. Combustion air inducer (CBI) was making splashing sound and rotating really slow. Previously i had condensation issue in August, water was dripping from CPI housing. Today I removed CBI and found it full of water so cleaning and drying it resolved the problem. Condensation is not 100% resolved, i will have to watch it next year.
 
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Old 09-16-11, 12:08 PM
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Originally Posted by ponti3800 View Post
just resolved similar issue. Combustion air inducer (CBI) was making splashing sound and rotating really slow. Previously i had condensation issue in August, water was dripping from CPI housing. Today I removed CBI and found it full of water so cleaning and drying it resolved the problem. Condensation is not 100% resolved, i will have to watch it next year.
Update - CBI is full of water again. That is not good, I might have serious problem and need to open furnace to find the problem. Any ideas will be appreciated.
 
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Old 09-17-11, 07:25 AM
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on the outlet of the CBI is a rubber boot looking trap with a hose coming off the bottom. Remove that whole piece and clean it out. Clean the hose as well.
 
 

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