Gas and Oil Home Heating Furnaces - gas furnace

Recently replaced limit switch because blower would not
shut off even though the burner did cycle on & off. Now
blower cycles on & off frequently, often running only a moment with only a moment between cycles, without turning the burner on. However, it does heat well. Other than this problem it seems to go through the heating cycle as it
should.

It sounds like the control points need adjustment. If the "ON" point is too low, and /or the "on" and "off" settings are too close together, the furnace fires....runs a bit & then when the fan switch starts the blower it almost immediately cools the switch enough to satisify it & de-energze the fan, however, since flames are on it is just a very short time until it r-closes starting the fan again. This can also be seen in normal operation if the home is very cold, & may continune until the room gets closer to normal tepmerature. Try setting the "on" setpoint about 135 F. and leave the off set point all the way down. Then operate the furnace for about 10 minutes to reach operating temperature & then turn thermostat off. Flames should extinguish. Now with blower still operating feel with your hand at one of the registers, as the furnace cools back down, if the air is still warm & shuts off, adjust "off" point slightly lower. If it continues to run after the air feel cool to the hand, adjust the "off" point slightly higher. Anytime air leaving the register is below body temp. a draft or "cold blow" complaint is likely, even tho there is useful heat still present. Never allow fan/limit dial face turn when adjusting on & off setpoits as calibration will be lost.