Furnace Question - master switch vs thermostat

Too often, and unpredictably, when the thermostat tells our gas furnace to turn on, all that turns on is the fan that exhausts the moisture from the combustion. It is not followed up with the flow and ignition of the gas.
If I flip off the master switch that controls power to the furnace, and flip it back on after a short time, the fan starts up, and the ignition always occurs.
But if I go to the thermostat and raise the temperature there, by breathing on it, for example, that shuts the furnace off; but when the temperature at the thermostat drops back to the ambient temperature, and the fan starts up again, ignition never occurs.
So it looks like there is a difference in what is shut off by the master switch and by the thermostat, and that the problem has something to do with that.
Any suggestions?
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There was a situation posted about a week ago, similar to yours. There is a really sharp guy called "hvactech2" who explained that this is called "lock out" which occurs when there is a problem sensed by the board in the furnace. By turning off the power and then back on, it will reset the unit, until it senses the fault again and locks out

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Which means: Get it fixed because there IS a problem. Dont wait till its 0 outside or you go away for a weekend. Turning the power off to the furnace resets the circuit board, basically like rebooting the computer. It keeps reoccuring because there is a "fault" happening within the furnace or vent piping. Turning the stat off does not reset anything because it does not restet the power to the main circuit board. Bubba
On Sun, 23 Jan 2005 10:41:49 -0500, "RBM" <rmottola1(remove

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