Our furnace won't turn off. I turned the heat off at the thermostat and no luck. I changed out the thermostat with a new one and it is doing the same thing. If the breaker is off, the fan and heat are off; is the breaker is on, the fan and heat are on even if the thermostat is set to off. We turned down the thermostat and the house just got hotter and hotter.

THis is a Lennox FAG, model G12RQ 3E-137.

This furnace was here when we bought the house; we estimate the age of the furnace at 20-22. It was originally wired so that the blower is on all the time, which is probably a good idea for a house with high ceilings ( some over 12' and 3 stories.