The line of people telling you what is wrong is pretty long already so I pass. Seriously,the problem can easly be found by a compident tech useing a VOM. Were I forced to take a guess,I would say the problem is with a tempature controled fan switch found just downstream of the heat exchanger. I don't reccomend replacing anything else before proving the need with a meter.

Did the tech tell you after seeing the system, or over the phone that it was the control board? If he didn't see it then maybe it wasn't bad.

Something to think about... when most modern gas furnaces try to fire up, they run a pre ignition check. It takes a several seconds but it lets the control board know if all the safety switches are closed, it triggers the inducer motor to run which triggers the pressure switch, then it powers the glow plug ( ignitor), gas valve opens, fires up, then flame sensor sends signal to control board that there is actually flame present. Blower fires up a minute or so after that.

With that said...depending on manufacturer ... if there is a problem in one or more of those pre ignition systems, the system tries to fire again... and then again. Usually after 3 times it will go into a "Lock out" ...shutting the heating part of the furnace off and turning on the fan motor. This is why you should get a qualified tech to come check your system out & replace the bad part or make whatever adjustment might be needed.

Hope this helps

This post was edited by fluffybunnysui on Tue, Mar 4, 14 at 9:17

RE: Help! the blower on my furnace will not turn off -- happened to me last week. I found a phone number on the furnace and they came out and fixed it for $155 - a service call and a capacitor.

Thanks to all of you that replied. It gives me something to do this weekend. The tech is coming over Saturday. So lets see what happens, I will let you know. Again Thanks !!