I have a older home with a older furnace. I started it up this fall and the blower continues to run after the house has warmed and the themostat has turned off. The blower runs and runs, blowing cool air. To stop it I have to turn off the main switch to the furnace. What do you think the problem is?? Please help, it's getting cold!!

Most likely it is the relay that switches it on and off. Follow the wires back from the blower motor to a little box. If you give it a tap, and the blower quits, you can be sure it is the problem. Shut the power off, note where which wires connect, and remove it. Take it to an electrical supply store and let them match it up.

It could also be the limit switch. After the heat shuts off, the blower continues until the furnace is cooled down and the limit switch opens. Again, the electrical supply should have a new one.