I know some of ya'll will be all over this with good suggestions.

Got a gas lennox furnace,and its been doing this off and on for several years.It kicks on fine,works great,but the blower won't always go off once the temp. is reached and the burners go out.Sometimes it stops after a minute,but other times the blower will run an hour or all day.If it dosen't go off,I trip the circut breaker.Turn the breaker back on later...couple hours or days,sometimes the fan will be right back on,others it won't go till the burners fire up again.

I'm guessing there is some type of faulty sensor or relay.Pretty soon the extra elec. cost will equal a service call,which I'm trying to avoid.

Older gas central system,filters are clean,and I replaced the thermostat last year hoping that would fix it.It didn't