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hube1iam 12-28-2011 07:22 PM

Intertherm furnace problems
I have an Intertherm LP furnace that often refuses to light. It generates tremendous condensation in the drain line. sometimes when I drain the water it will start other times not. i've had two service calls and each time it works for awhile after they leave. This last time the problem was diagnosed as a pressure switch and it was replaced. within two hours the furnace stopped igniting again. I'm wodering if the problem might be the venting. The vent rise vertically with 2 45 degree elbows and then the exhaust vent goes horizontal for a few inches then drop about 6" creating in effect a trap for the condensation. The vent runs horizontal for about six feet then goes vertical. The fresh air return comes from the vertical segment. This exhaust vent arrangement does not seem right to me and the technician I used seems not to know. Is there any chance this could be plumbed incorrectly or does this "trap arrangement" sound right?
Thanks for your help

ben's plumbing 12-28-2011 07:26 PM

would really need a picture of what you are talking about...

Doc Holliday 12-28-2011 07:27 PM

it very ewell could be. When a pressure switch is indicated it revolves around the exhaust as well.

If a bird made a nest in your exhaust (pipe) , a pressure switch diagnostic code would flash.

hube1iam 12-28-2011 07:30 PM

I'm thinking the trap hold the condensation so that it will not breath therefore over time the pipe fills up with water and restricts the exhaust. could that be.

REP 12-28-2011 07:34 PM

Clearly needs a picture of that "trap"in order to evaluate.

yuri 12-28-2011 07:40 PM

Post some pics if you can. There should not be ANY point where water can get trapped.

Doc Holliday 12-28-2011 07:53 PM


Originally Posted by hube1iam (Post 805961)
I'm thinking the trap hold the condensation so that it will not breath therefore over time the pipe fills up with water and restricts the exhaust. could that be.

yes. definitely. These other guys are far more experienced with this than I but yes, definitely.

hube1iam 12-28-2011 07:57 PM

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I'm not sure you can see this. If not i'll try again. i apologize for the quality of the attachment

ben's plumbing 12-28-2011 08:04 PM

can't really see all that well but it looks like just what you are saying its traping water.....thats a no no

REP 12-28-2011 08:14 PM

Well Thats your problem.The vent must constantly be rising as it travels to the chimney.
That picture didn't really show what the vent was made of.It could be single wall metal,double wall metal ("B"vent),normal PVC or the outlawed high temp plastic.
Traps are for water,not for flue gases.

hube1iam 12-28-2011 08:23 PM

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I'll try again

hube1iam 12-28-2011 08:25 PM

The vents transition from PVC to ABS then back to PVC

yuri 12-28-2011 08:27 PM

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Is there only 1 pipe exiting the roof. Looks to me like you have a concentric exhaust kit ( pipe within a pipe). Still there should be NO trapping and the installer offset it to make it fit. Will never work properly like that.

Concentric kit.

hube1iam 12-28-2011 08:30 PM

I don't think there is a pipe within a pipe as several years ago the piping came apart and dumped water on my ceiling. I repaired the connections but left the alignment alone. Actually I think the roof unit might look like that. i'll need to check in the morning. Thanks ALL

REP 12-28-2011 08:32 PM

Then remove the whole trap thing and replace with a stright piece of PVC with couplings.Make sure to be quick aqnd twist the couplings that are glued up .You have to be quick because that PVC glue sets fast.You want to twist the coupling to make sure there is a complete circle of glue under thwe coupling so that vent gases have no place to escape.

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