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Discussion Starter · #1 ·
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
 

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I'm Your Huckleberry
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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.
 

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Discussion Starter · #4 ·
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.
 

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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.
 

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Hvac Pro
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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.
 

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Discussion Starter · #14 · (Edited)
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
 

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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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You may have to be VERY careful how you fix that piping and not alter it. Miller/Intertherm especially their mobile home or pre fab home units are very specific to using their concentric kit. They finely tune the combustion air supply and pressure switch settings due to them being so compact. I would want to get the install manual and see what methods they have for venting it. You may be able to go with a conventional 2 pipe thru the roof arrangement and get rid of that mess but you need to follow the original install info if they allow a 2 pipe setup.
 
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