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Old 12-06-2009, 11:40 AM   #1
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Furnace condensate drain/trap issue


I am scratching my head over a condensate drain/trap issue with our ICP 90+ efficiency furnace. I recently replaced the drain line from the furnace vent to the trap because the original rubber hose deteriorated and was leaking. (I replaced it with a different material (clear vinyl) because that was what I could find in the proper size.)

Furnace condensate drain/trap issue-inside.jpg

Furnace condensate drain/trap issue-trap-drain-pump.jpg

I am having a problem with that line not draining properly. It is easy to see because the hose is a clear material. After the furnace runs for a while the hose will fill up with condensate, even though it is higher than the trap. It acts like there is some kind of airlock on the line preventing it from draining. It will eventually fill up enough to cause the unit to kick out and display an error code which is for a soft lockout, one of the potential causes being "Condensate drain blocked".

Furnace condensate drain/trap issue-inside-trap-h2o.jpg

I have removed the trap from the furnace and taken it to a service sink and flushed it out from both directions. Water seems to flow easily through the unit when I am doing this. I plugged various ports with my fingers to force water through all the different openings in both directions - no noticeable restrictions.

The furnace has a concentric vent setup for combustion air/flue exhaust. Everything appears OK with that - no external blockage and the exhaust seems to be exiting properly with decent velocity.

All piping (furnace vent and condensate drain piping) appears to be sloped correctly.

The 5/16" line from the center pressure tap on the trap is clear - I can disconnect either end of the hose and blow back into the combustion chamber or out through the trap itself.

The interesting thing is that water will collect in the clear tube prior to the trap, and it will stay in that tube until I remove the cap on the top of the trap that corresponds to the same line (with the red clamp in the picture below). If I remove the cap that corresponds to the line coming from the combustion chamber (green clamp in picture below), nothing happens to the fluid in the vent drain line. If I remove the small diameter pressure tap line that connects to the top of the plastic transition (combusion) chamber nothing happens as well, even if I gently blow or suck on the hose.

Furnace condensate drain/trap issue-trap.jpg

I can duplicate the problem by disconnecting the line from the vent and pouring water into it. It will back up from the trap into the line and will stay there until I remove the cap, which some how vents the trap and releases the water, and it will drain freely through the trap down into the condensate pump catch tank.

Furnace condensate drain/trap issue-drain-disconnect-retain-water.jpg

I don't understand why the trap is holding back water in that line? I have flushed the trap as well as I can, although the PVC drain pipe is glued to the outlet of the trap, and I only saw a small of debris come out of it when I first flushed it out. I even added a small vent hole in the PVC pipe downstream of the trap (upstream of the condensate pump) to make sure that there wasn't any kind of vapor lock in that pipe (although that wouldn't make sense because the other drain line coming from the combustion chamber doesn't seem to be backing up at all).

Furnace condensate drain/trap issue-drain-relief-hole.jpg

I'm befuddled. I keep coming back to something being wrong with the trap, but for the life of me I can't figure out what the problem might be. Maybe the interior of the trap is more complicated than I am picturing it in my head and something is going on inside of there??? Could there be something going on with the small 5/16" pressure line that I don't understand? Can anyone explain exactly how this trap operates if it is different in some way from a standard pipe trap? Any suggestions before I spend the bucks for a new trap or a service call?

TIA!

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Old 12-06-2009, 01:11 PM   #2
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Furnace condensate drain/trap issue


Cut the trap out and soak the whole thing in a bucket of strong bleach/Javex for an hour and then flush it. I would cut the horz pipe after the trap, then go to HDepot and get some large clear hose to cobble it back together.

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Old 12-06-2009, 07:26 PM   #3
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Furnace condensate drain/trap issue


So just having some additional buildup on the inside walls of the trap can cause these symptoms? Even though I appear to get good flow through the trap by forcing tap water through it? Interesting.

I'll probably just pick up a 3/4" PVC coupling and cut the horizontal drain line about where the tie wrap is on it right now, then glue it back together.

< edit to add: >
So Javex is just regular bleach? Just like Clorox? I thought at first it was something special until I did a search.

Last edited by SteveC; 12-06-2009 at 07:31 PM.
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Old 12-06-2009, 07:29 PM   #4
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Furnace condensate drain/trap issue


Does the drain pipe go down to deep into the condensate pump. You could try putting a bucket there to see what happens. The drain pipe should be above the water level. The drain pipe should only be into the pump about 1/8 ".
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Old 12-06-2009, 07:44 PM   #5
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Furnace condensate drain/trap issue


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Originally Posted by marchvac View Post
Does the drain pipe go down to deep into the condensate pump. You could try putting a bucket there to see what happens. The drain pipe should be above the water level. The drain pipe should only be into the pump about 1/8 ".
I was wondering that same thing earlier today and I have already shortened the pipe some. It's definitely still quite a bit more than 1/8" into the pump reservoir though (more like 3/8" to 1/2"), but to test the idea I finagled the pipe out of the pump completely and let it drain onto a towel while the furnace was running, and even so there was water backed up into the hose upstream of the trap. That test, along with adding a weep hole in the top of the PVC drain pipe (see last photo in the original post), kind of eliminated that as a potential issue in my mind. I'll go ahead and shorten the drain pipe some more just to be sure that it is above the water level in the pump, but I don't think the problem lies there.

Thanks for the suggestion though.
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Old 12-06-2009, 08:04 PM   #6
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Furnace condensate drain/trap issue


The thin black hose vents the trap and is probably a critical sized opening inside the port at the trap and the ventor fan. Siphoning is very tricky and it does not take much to slow it down. May have to take a paper clip or small bit and ream out the port on the ventor fan, can get a sulphur buildup there. Getting more calls with algae built up inside traps as it does that during the Summer when there is no flow. Did you check the intake part of the concentric? If you can carefully pull the hood off check inside for spider webs. If it wont easily come apart stick your fingers in there and use a bottle brush.
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Old 12-06-2009, 08:20 PM   #7
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Furnace condensate drain/trap issue


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Originally Posted by yuri View Post
The thin black hose vents the trap and is probably a critical sized opening inside the port at the trap and the ventor fan. Siphoning is very tricky and it does not take much to slow it down. May have to take a paper clip or small bit and ream out the port on the ventor fan, can get a sulphur buildup there. Getting more calls with algae built up inside traps as it does that during the Summer when there is no flow. Did you check the intake part of the concentric? If you can carefully pull the hood off check inside for spider webs. If it wont easily come apart stick your fingers in there and use a bottle brush.
When you say "...ream out the port on the ventor fan..." I presume you're talking about where the small hose attaches to the fan plenum (see photo)? I'll try cleaning that out.

Furnace condensate drain/trap issue-inside1.jpg

As far as the concentric, I did not try to take it apart. I felt around on the inlet side as best I could, and removed a couple of small old leaves, but didn't detect any major blockage. I'll try taking it apart (carefully) and check that when I get back into town on Tuesday.

Thanks again.

< edit to add: >
"...algea inside the trap..." explains the bleach. Thanks.

Last edited by SteveC; 12-06-2009 at 08:23 PM.
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Old 02-22-2011, 12:46 PM   #8
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Furnace condensate drain/trap issue


Did you ever find the problem.
I've been dealing with this problem for years.
It's been once a month that I've had to restart the thing.

Did you have to buy a new trap?

Looking at the pictures of your furnace, I thought I was looking at my own furnace.
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Old 02-22-2011, 01:16 PM   #9
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Furnace condensate drain/trap issue


Quote:
Originally Posted by yuri View Post
The thin black hose vents the trap and is probably a critical sized opening inside the port at the trap and the ventor fan. Siphoning is very tricky and it does not take much to slow it down. May have to take a paper clip or small bit and ream out the port on the ventor fan, can get a sulphur buildup there. Getting more calls with algae built up inside traps as it does that during the Summer when there is no flow. Did you check the intake part of the concentric? If you can carefully pull the hood off check inside for spider webs. If it wont easily come apart stick your fingers in there and use a bottle brush.
That plastic is made to resist build up so it can be washed out easily.

Did you notice the tube up hill rise over the blower door switch? That could be your only problem.
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Old 02-22-2011, 01:20 PM   #10
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Furnace condensate drain/trap issue


Push come to shove you could eliminate that plastic trap and buy one or fashion a new trap with PVC elbows.

I am dealer for the brand of furnace you have.
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Old 02-23-2011, 09:58 AM   #11
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Furnace condensate drain/trap issue


Where/what is the blower door switch?
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Old 03-23-2011, 11:15 PM   #12
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Furnace condensate drain/trap issue


If Im not mistaken isnt that plug with the red clamp supposed to be open so the trap can vent properly.The only thing that can go wrong with a p trap is not installed correctly with the vent and or it getting plugged up.I think your not letting it vent properly after the trap does its job.It fills up than it cant drain into the sump.
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Old 11-02-2011, 08:17 PM   #13
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Furnace condensate drain/trap issue


I had the same issue with my furnace. All that was needed was $1 in shims. The furnace needed to be pitched just a little towards the drain hoses. When the furnace shuts off and the suction stops the water drains. I couldn't believe it was that simple....
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Old 11-02-2011, 08:44 PM   #14
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Furnace condensate drain/trap issue


Quote:
Originally Posted by pmahar
I had the same issue with my furnace. All that was needed was $1 in shims. The furnace needed to be pitched just a little towards the drain hoses. When the furnace shuts off and the suction stops the water drains. I couldn't believe it was that simple....
Its not.....
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Old 11-02-2011, 11:14 PM   #15
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Furnace condensate drain/trap issue


Quote:
Originally Posted by PeteMc View Post
Did you ever find the problem.
I've been dealing with this problem for years.
It's been once a month that I've had to restart the thing.

Did you have to buy a new trap?

Looking at the pictures of your furnace, I thought I was looking at my own furnace.


Totally agreed!Maybe you just need a new trap!




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