Oil Furnace Short Cycling


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Old 02-21-13, 06:21 AM
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Oil Furnace Short Cycling

Our old Luxaire oil furnace is short cycling, but on the low end. It heats up to the temp required to turn the blower on, but then within a few minutes, it cools off to where the limit switch drops back down to 90 and shuts off the blower. The furnace does this 2 or 3 times, then completely shuts off. I have checked and cleaned air filter, nozzle, fuel filter at the tank. Bypassed the tstat, checked and cleaned the blower motor, and even replaced the limit switch. I am not sure what else I am missing that could be the cause. Any ideas?
 
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Old 02-21-13, 06:37 AM
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There is a small kink in the fuel line, but it does not seem to be hampering it as I get a nice flame in the fire pot.
 
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Old 02-21-13, 04:12 PM
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The fan is controled by the temperature of the air passing over the heat exchanger. I wonder if the firing rate of the furnace has been reduced (smaller than spec'd nozzle)?

Did the same thing happen when you by-passed the stat?
 
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Old 02-22-13, 08:24 AM
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Yes same thing happened when I bypassed the stat. Replaced the nozzle and the electrodes yesterday even though I was not having an ignition problem. Bought a new Pro digital stat and installed that, even though the old mercury stat still worked. It was due for replacement. Furnace cycled and worked fine through the night last night. This morning it started doing the same thing again. Wondering if the heat exchange is sooted or if my barometric dampener is not set right allowing too much heat to be pulled into the chimney causing my furnace to cool down too quickly, hence the cycling.
 
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Old 02-23-13, 04:39 PM
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Is the correct nozzle installed (the one the furnace manufacturer specs)?
Is the pump pressure right?
What speed is the fan set on for heat?
 
 

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