Original message
| alydar66
 |  "Furnace Trouble"
, posted Tue 11 Nov 20:41  
Im having a problem with my furnace that no one can seem to diagnose. Can some of you techs out there take a look at this and give me an idea of what you think might be the problem? This is a Bryant gas-fired, induced combustion furnace.
This is the order that things happen:
1. Furnace is working properly. Its 45 degrees outside and the furnace only has to stay on for short periods of time to keep the house temp. at the thermostat setting.
2. Temperature outside drops to 30 degrees overnight so now the furnace has to stay on for longer periods of time to keep the desired house temperature.
3. Sometimes the furnace will shut down before temperature on thermostat is reached. It shuts down in this order:
a. inducer motor shuts off
b. furnace flame goes out
c. main blower shuts off after a couple of minutes
4. Furnace attemps to restart in this order:
a. inducer motor starts
b. Im assuming pressure valve closes because I have tested it and it seems to work properly.
c. pilot sometimes lights and sometimes doesnt.
d. inducer motor stops. Sometimes the pilot will stay on when the inducer motor stops, other times it
goes out.
e. inducer motor starts after a few seconds and the whole process is repeated.
f. eventually the furnace will light. Sometimes it takes up to 15 of these cycles for the furnace to light.
g. after the furnace lights, sometimes it will stay on for only 15 seconds and other times for 15
minutes other times in between.
5. If I shut the furnace off for a half hour or so and restart it, it will start and run fine. At some point, I
believe something gets to hot and shuts down the furnace, and the whole cycle starts repeating.
6. My schematic shows 1 Limit Switch and 1 Auxilliary Limit Switch, both are manual reset.
7. Ive replaced the Standing Pilot, the Inducer Motor circuit board and the Blower Motor board.
Does anyone have any ideas what could be causing the problem? Could the gas valve be causing this problem?
Thanks for any help.
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Replies:
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| bubbad
| "Re(1):Furnace Trouble" , posted Tue 11 Nov 23:12
Can you post the make and model # of your furnace?
The inducer shouldn't be the first thing shutting off during the heat cycle. I would monitor it and see if it's drawing too many amps, or maybe bearings are getting tight while it's running.
Can you tell if the inducer sounds like it's at full speed all of the time?
bubbad
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| | alydar66
| "Re(2):Furnace Trouble" , posted Wed 12 Nov 10:17
This is a Bryant model #376B. Its a pretty simple Downflow, Gas-Fired, Induced-Combustion Furnace. Its about 20 years old.
The inducer motor is fine. For some reason, something is telling the inducer motor to shut off. I just cant figure out what's happening that makes it shut off.
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| | wondering
| "Re(2):Furnace Trouble" , posted Tue 11 Nov 23:42
Just a wild guess, the heat exchanger is cracked or rusted open.
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