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Old 10-17-2009, 09:33 AM   #1
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Gas Furnace Power Venter Problem


Hello, everyone.

I have this power vent kit on my gas furnace:

http://www.fieldcontrols.com/pdfs/46285100.PDF

Actually, the vent itself is different, but the control box is the same.

Sometimes my thermostat turns on the furnace, but the control box won't turn on the blower. I had a repairman come out a couple years ago, and he simply tapped on the box and got it working. He said the sensor in there can get gummed up in such away that it's not sensing that the vent is working. Tapping it can ungum it. I've done that successfully a few times since then, but it's a hassle to go down in the crawl space, and I'm afraid it will happen in the middle of a cold winter night or when only my wife and baby are at home.

How can I fix this so I'll never have to tap that box again?

I pulled the main cover off, and the wiring looks secure on the terminals. I didn't know how to get the cover off the Honeywell cylinder on the side. I assume the sensor is in there. I also wasn't sure how to disconnect the white wire from that cylinder. Does it screw off or pull off?

It's worth noting that the whole set is about 4 years old, so it was pretty new when this first happened. Also, the contractor hired to install the vent system did some pretty sloppy work. The previous owner hired some pretty cheap guys to do the repair work necessary before we moved in. We should have just asked for the cash and fixed things ourselves.

Thanks for any advice you can give me.

Steve.

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Old 10-17-2009, 10:02 AM   #2
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Gas Furnace Power Venter Problem


Personally/IMO from what you have described the whole thing looks very unsafe to me. If the sloppy contractor did not setup the Barometric control properly your furnace can produce CO and that is incredibly dangerous. That Barometric should be checked annually by a tech with a manometer and a lot of experience. Where do you live? With a small baby I would put safety first and consider a different type of furnace. If the basement does not go below 32F you may be able to have a high efficiency gas furnace installed and vented thru the wall. Or you can go with a horizontal electric furnace depending on your electric costs.

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Old 10-17-2009, 10:18 AM   #3
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Gas Furnace Power Venter Problem


Hi, Yuri.

Thanks for the advice. I agree that safety needs to come first.

We have CO detectors and a gas detector installed in our house.

I believe a working power vent control sensor prevents the blower from turning on if the vent isn't working. Actually, ours prevents the blower from turning on even if the vent is working sometimes. Either way, this should keep CO from coming into the house, right? The CO detectors have never detected anything.

I'd like to put off installing a new furnace for a while if I can. It would be great to get this control box fixed if it's as simple as taking it apart and cleaning it out or lubricating something.

Thanks again for your advice.

Steve.
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Old 10-17-2009, 12:47 PM   #4
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Gas Furnace Power Venter Problem


I studied the wiring diagram and the control energizes the gas valve thru the pressure switch (if the installer wired it properly). Has nothing to do with your furnace blower. That is turned on by the furnace controls. The pressure switch may be sticking and the tubing etc to it need cleaning. CO detectors are a HUGE misconception. They are designed to alarm at a higher than healthy threshold for your baby. CO is 10 to 100 times more toxic to an infant as they have 1/10 th the amount of blood as an adult. Therefore it is far more concentrated to them. CO detectors are designed for a major/catastrophic event like a blocked chimney, NOT to tell you when to change the furnace. OSHA has recommended allowable CO readings over a period of time. CO detectors deteriorate over time and I would not trust my health to them. I have a $200-$300 CO detector for my job and the gas company has a $1000 model which detects down to 1 ppm consistently. The average WalMart $30 detector cannot be as reliable and sensitive due to the cost. You get what you pay for in sensitivity and accuracy/reliability.
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Old 10-17-2009, 07:01 PM   #5
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Gas Furnace Power Venter Problem


Wow, Yuri, thanks for the help!

I'll look at the pressure switch. Thanks for the CO information, too!

Steve.
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Old 10-17-2009, 08:07 PM   #6
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Gas Furnace Power Venter Problem


It isn't the pressure switch.

A. If the furnace inducer is coming on without the power venter running, its wired wrong.
B. Its the sequencer(they call it a delay relay) that causes most no heat calls on those units. And tapping on the box, just rattles the relay, and it starts to work again.
C. If the pressure switch is getting gunk in it. You have more troubles then you know. And it then needs to be set up properly.

D. CO detectors are a security blanket(something that falsely makes you feel secure). DO NOT rely on them to keep you safe. Some won't trip until CO levels are well above safe levels.
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Old 10-17-2009, 09:05 PM   #7
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Gas Furnace Power Venter Problem


Probably the sloppy contractor never set the Barometric OR the pressure switch setpoint properly and safely. If it does not have enough draft the furnace could be carboned up also. Probably not wired properly.

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