I just noticed that regardless of whether the FAN switch is in the AUTO or ON position, the fan is continuously running. It just started to do this, this past week, up until now it was fine, only running when the furnace kicked in.

When I turn the SYSTEM switch from HEAT or COOL to OFF, it still continues to run.

Any help will be appreciated - I'm trying to save on a service call, if it's something I can fix myself.

Thanks.

Problem is in the furnace/air handler fan contol, either a relay or a PC board. A tripped limit will do this in many furnaces to.

So, replacing the thermostat will not fix this problem?