natural gas furnace won't stay on


I have a natural gas furnace that won't stay on. The pilot is lit and the burners come on, a few seconds later the fan starts and runs for no more than a minute and then it stops. The burners sometimes go out before the fan stops or the fan never comes on at all. I can turn the fan on at the control and have it run with out a problem, but that is just circulating the air and not heating it. I think the fan is controlled by it's own thermostat. Once the thermostat in the house starts the burners a thermostat in the furnace turns on the fan when it reaches a certain temp to blow the warm air through the ducts. Does this sound right? Could this be where my problem lies? Could it be as simple as a loose wire to that particular thermostat? We had a service guy come and look at it and tell it us it's just old & inefficient and it'll be about a grand to replace. I had the Gas Company out last week to replace my meter with a higher flow model due to a recent swimming pool installation. He checked all our gas appliances after the replacement and everything including the furnace worked fine. The furnace started having trouble over a week later, I doubt the problem was caused or triggered by anything he did since the furnace worked fine for over a week. Help a cold Californian please, yes it gets cold in CA. I'm in SoCal, high desert area, last weekend we had single digit temps (rare). Thank God it worked then.
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in buffalo ny: on my 1990 gas boiler, the spark ignitor is also a flame sensor. on mine i have to see that pilot flame wraps around the sensor/ignitor/thermocouple properly after the ignition spark and during the main burner on. and exactly according to the specifications of the manufacturer. i keep my manual by the boiler. if there is a good flame then i replace the ignitor/sensor. if i have insufficient flame, i clean out or replace the pilot assembly. see: http://www.arnoldservice.com/Troubleshooting_Heating_Problems.htm and: http://toad.net/~jsmeenen/gasvalve.html
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snipped-for-privacy@aol.com wrote:

There's a safety thermostat in the furnace that is intended to shut down on furnace overtemperature. If yours is failing or has a loose connection, it might be the culprit. Or you could just replace the whole furnace. Or move (further) south.
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snipped-for-privacy@aol.com wrote:

Could be the fan control is set too high and just needs tweaked down a little. -Felder
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