Ok my blower just turned on, my propane furnace and it's not in operation due it being summer. My thermostat is set at 65 and the room temp is 78. The heater never actually fired it was only the blower that ran and continued to run till I tripped the breaker. Any ideas on what caused it?

  • Some modern electronic controllers cycle the fan on to increase air circulation for comfort. Check your owner's manual.
    – Rob
    Jan 27, 2016 at 14:06

2 Answers 2


If your power flickered, that might have confused the furnace's electronics. Otherwise, your furnace might possibly have an automatic periodic purge to keep condensate from forming & the burners / blower from rusting.

Which make & model furnace do you have? If yours supports periodic purges, that should be mentioned in the owner's manual (available online).


Which blower?

If it is the flue blower, that is managed by the electronic controller. Cycling power (by flipping off the circuit breaker for a few seconds) to reset the logic is worth a try. Otherwise, there is a fault in the electronics which is probably best fixed by replacing the control board.

If it is the ventilation blower, first check the room thermostat. It is possible it is set to "fan always on". Otherwise, the fan is controlled by a thermal sensor somewhere on the firebox. If it is a one speed blower model, it is almost certainly a simple thermal contactor. Inspect and replace. If it is a variable speed blower (typical on high end furnaces), it is a sensor connected to an intelligent controller. Check the maintenance instructions to see if there is direction. Otherwise, the "shop manual" is needed for a DIY repair.

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