The blower fan on my electric furnace will not shut off without tripping the main breaker switch. It is an older furnace that had not been used all too often as I generally use a wood/coal stove for heating, but had been operating properly when I have used it. The last time it was used , the thermostat was set for 70 degrees but when I noticed, it was at 75 and the furnace was still running. The only way I could shut it off was by the main breaker