OT: Gas furnace venting, changed roof stack

Anonymous-0 · Nov 13, 2008

Hi Guys,

Need your help...had a new roof put on house, including a new flue stack that goes out through the roof.(only the 36 inch part that goes through roof. Now furnace wont run..inducer motor runs, but wont fire. It is flashing a code indicating a pressure problem...possible reasons "blocked flue" or "high winds"
PRSSURE, DRAFT SAFGUARD, AUX-LIMIT SWITCH(WHEN USED)OR BLOCKED VENT
SWITCH(WHEN USED) DID NOT CLOSE OR REOPENED (DOWNFLOWONLY)
If open longer than five minutes, inducer shuts off for 15 minutes
before retry.
Check for:

* proper vent sizing
* defective inducer motor
* restricted vent
* excessive wind
* low inducer voltage(115VAC)
* defective blower motor or capacitor
* defective pressure switch
* inadequate combusstion air supply
* disconnected or obstructed pressure tubing

Any ideas? Would the new vent pipe cause this?

Thanks in advance!

Mark

Goose · Nov 13, 2008

Just as an experiment, take the rain cap off and see what happens.

When our house was new, for the first couple of years sometimes when we had a strong northwest wind the pilot on the water heater would blow out. It's a sealed combustion chamber and hard to light. I finally replaced the rain cap with a different design and the pilot hasn't blown out since.

El Toro · Nov 13, 2008

If they removed the old roofing material, some of that may have fallen into the furnace blocking the flue/exhaust. Hal

Christopher S. · Nov 13, 2008

Does your vent pipe have a horizontal section in it?

I have seen it before that when a roofer installs a new vent pipe he actually pushed down on the vent pipe that was in the building. This caused the horizontal section that was in the house to run "down hill". In one case the exhaust would push its way up the pipe until it got to near roof line and then would condense. The water would run back down and now get stuck on the horizontal section that is now running down hill. After a while of this the down hill section actually started acting like a sink trap and filled with the accumulated condensation. This did not allow any of the exhaust to get past. This resulted in an error code of a blocked flue.

Anonymous-0 · Nov 13, 2008

Check that the chimney is tall enough. If not turbulance from the roof can blow down it once in a while. Also check that the intake is clear.

M w J · Nov 13, 2008

Mine had a slimed up water drain They are suppose to hold a little water in a gooseneck like fitting. But that water grows alge over the summer so it won't drain then it lets water stand at the bottem of the vent pipe so airflow was cut in half then they wont burn. Pull the little rubber water drain hoses off of the bottem heat exchanger and see if water runs out.

Lesformore · Nov 13, 2008

I take it the furnace ran fine before the vent was changed. It appears you have a blockage in the flue. Test this by disconnecting the flue at the furnace and trying to start it. If it runs, turn the power off to the furnace. This proves the vent is plugged at least partially. If it won"t go there could be a problem with the inducer fan. This fan has to produce a vacuum in the combustion chamber and a diaphragm switch which will then start the firing sequence. Anything stuck in the fan blades will prevent it from doing this.

Farmedic · Nov 13, 2008

I have this problem about once a year, I have found that it is where the vacum hose attaches to the fan, if I take the hose off and run a small piece of wire into the fitting and clean it out it will go back to working. On mine I tried many diffrent things before I found this.

JDB · Nov 14, 2008

Found the same problem in mine a couple nights ago

OT: Gas furnace venting, changed roof stack

Anonymous-0

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Goose

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El Toro

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Christopher S.

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Anonymous-0

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M w J

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Lesformore

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Farmedic

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JDB

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