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homer12 12-14-2006 06:09 PM

Bryant gas furnace non startup
11 year old Bryant upflow standing pilot furnace. Pilot is lit, thermostat calls for heat, inducer fan comes on... and that's it. It just sits there with the inducer running merrily along. There is no change in the pilot and I don't hear the usual fairly loud sound of the gas valve opening. Bad flame sensor? Bad circuit card? Is there a logical way to isolate the problem?

You guys seem to have a lot of knowledge about these things. Thanks for any input!

homer12 12-14-2006 07:01 PM

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I did a bit of troubleshooting and I think I found the problem. There is a sensor in a small box that is connected by a tube to the hood over the pilot. It looks like the path that the pilot exhaust takes to get to the flue. I guess it is a temp sensor? Anyway, I turned off the power to the furnace and an ohmmeter showed that it was an open circuit across the terminals of the sensor. So I installed a jumper across the 2 wires that connect to the sensor, flipped the breaker back on, and pushed the door switch. Voila, the furnace fired right up. So it looks like this sensor is bad. I bench tested it with a lighter and it still showed open circuit. Here is a picture of the little bugger. What temp should it need to close? Where can I get one?

homer12 12-14-2006 07:05 PM

one more pic
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The sensor from the other side.....

homer12 12-14-2006 07:46 PM

fixed, I hope
After fiddling with the sensor I pushed the spring loaded thing protruding from the back and lo and behold I got continuity. Then I checked it with a cig lighter flame again and I head a switch sound and got an open circuit. So I surmise that this is an OVER temp safety switch and by pushing the contact I reset it. I reinstalled it and the furnace is working great. Not sure why it tripped in the first place but I'll keep a close eye on it for awhile. But for now, all is good. :-)

#CARRIERMAN 12-14-2006 08:30 PM

Hi homer12

Let me take a crack at answering your answers. The limit that you have pictured is a flue limit. This as you have found out is a resetable limit. This particular limits job is to monitor the flue draft. What could have caused flue limit trip, or what is the most common cause is high wind. The other possibilitys are flue cap crushed by roofers, birds nest in chimney if attached to brick flue, squirrel in chimney or flue pipe, or even a high pressure differential in the house for some reason. Exhaust fan in window while sanding sheetrock or something of that nature. Never the less, if limit continues to trip. Please have the above mentioned checked. As a service man I cannot stress enough about having systems checked by "QUALIFIED PROFESSIONAL", the money it cost to get a good technician is nothing in comparison for the possible loss. Do your homework when selecting your servicing company. Don't just higher the first cheapo to answer the phone.

Good luck

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