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Condensation in Ignition Intake

Steveking8 Member Posts: 5
It's my 5th winter in my house and my furnaces 7th. I came home to cold house the other day and after some simple thermostat troubleshooting called the experts. They came out and determined that my Honeywell SV9541 gas valve had gone bad (condenser motor would not even fire) and replaced it.

The furnace worked great for about 5 hours then stopped igniting. The condenser motor would fire and the pilot would light but the burners would not. After watching it for a few cycles I noticed some water on the igniter plug where it plugged into the brand new gas valve. I shut the power off dried everything really well and turned it back on, everything fired up right away as it should. Another 5 or 6 hours later it went out again, opened it up and bingo, water on the plugs. After some investigating I determined that the water was coming in the combustion intake and dripping down on to the plugs. After some reading online I decided to install a water trap tee in the intake pipe fairly close to the furnace (see picture). That solved the problem, it's catching maybe a cup of water a day and I have had no other issues since installing it.

So that problem is solved, but now my question... Why did this start happening all of a sudden after 7 years? My furnace is an Arcoaire n9mp2050B12B1 and is horizontally vented with a concentric vent kit. I have looked outside for any blockage and even pulled the concentric vent w/ vent tube attached out of the larger intake tube, everything looks clear, and the intake tube is even dry inside. One thing I have noticed is that it seems there is a lot of condensation coming out of the vent, which I'm sure is normal, I have a grill in the area (not blocking the vent) and I am seeing ice build up on its cover. Thinking it could be a blocked drain I have pulled all hoses inside and outside of the furnace and made sure they are clear. I am getting a steady drip of condensation out the drains, so that seems normal.

So after a lengthy discussion, my question again. Why is this happening all of a sudden after 7 years? Could something else be broken that I am over looking?

Thanks in advance,



  • Tim McElwain
    Tim McElwain Member Posts: 4,588
    Do you have

    a condensate pump anywhere? I can't make out any in the photo, it looks like the condensate is trapped having to rise vertically quite a distance.

    Sometimes when something is installed incorrectly it takes a while for a breakdown internally. Check your Installation and Operating manual to make sure everything is correct. 
  • TomS
    TomS Member Posts: 61
    Intake air

    If you are getting that much water in the intake air piping I would suspect that you may have a leak in the concentric vent where some of the exhaust is being sucked into the intake. To prove this test some of the water you are collecting in the trap and see if it is acidic with some litmus paper.   In any event an exhaust leak is not good and who knows where else the exhaust is leaking to.  Make sure you have some CO detectors in your home and if it is in fact leak get it repaired ASAP.
  • Tim McElwain
    Tim McElwain Member Posts: 4,588
    If there is a break

    in the concentric vent between air intake and exhaust the burner would be affected by cross contamination drawing CO2 back into the combustion chamber. This would drastically affect the combustion.
This discussion has been closed.